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THE  SUN: 

ITS   CONSTITUTION; 

ITS  PHENOMENA; 

ITS   CONDITION 

BY  NATHAN  T.  CARR,  LL.D., 

JUDGE  OF  THE  NINTH  JUDICIAL  CIRCUIT  OF  INDIANA. 


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THE  SUN: 

Its  Constitution;  Its  Phenomena;  Its  Condition. 

BY  NATHAN  T.\£ARR,  LL.D., 


OF   THE    NINTH   JUDICIAL   CIRCUIT   OF   INDIANA. 

WITH    AN    APPENDIX. 

COPYRIGHT,  1883,  BY  N.  T.  CARR. 


PREFACE. 


The  treatise  here  presented  was  not 
originally  designed  for  publication  in 
this  form,  but  as  a  chapter  in  a  more 
extended  work  on  the  "Evolution  of 
Worlds,"  now  in  preparation.  Its 
present  publication,  as  a  separate  es- 
say, is  by  request,  to  which  the  author 
has  given  his  assent  the  more  readily 
as  he  hopes  that  his  views  upon  the 
important  subject  here  discussed,  be- 
ing presented  to  the  public  now,  may 
win  for  the  main  work,  when  it  shall 
be  completed,  easier  access  to  the 
minds  of  intelligent  readers. 

The  purpose  has  been  so  to  treat 
the  subject  that  the  essay  can  be  un- 
derstood by  readers  who  may  know 
nothing  of  the  technical  terms  used 
in  a  scientific  study  of  the  Sun,  and 
who  know  but  little  of  even  the  most 
elementary  facts  developed  by  those 
who  have  pursued  that  study ;  yet  it 
is  hoped  that,  modest  as  are  the  pre 
tensions  of  this  little  work,  it  will  not 


be  deemed  even  by  the  scientist  to  be 
unworthy  of  his  attention. 

The  forces  and  laws  of  matter,  as 
known  to  us  here  on  the  earth,  are 
made  the  basis  upon  which  every  pos- 
tulate and  conclusion  are  made  to  rest, 
and  all  speculations  not  actually  com- 
pelled by  our  knowledge  of  these  laws 
are  strictly  avoided.  Attraction  is 
recognized  as  the  primary  cause  of 
every  feature  observed  in  the  Sun, 
producing  the  exterior  crust  (photo- 
sphere) by  concentration,  and  by  con- 
tinuance the  interior  heat,  from  whose 
repulsive  or  expansive  force  come  the 
interior  gas^s,  eruptions,  sun-spots  and 
chromosphere. 

While  it  was  impracticable  to  con- 
fute in  detail  each  of  the  erroneous 
theories  which  have  been  advanced 
concerning  the  Sun,  yet  it  is  believed 
that  the  exposition  here  offered  of  its 
constitution,  condition  and  phenom- 
ena affords  a  criterion  of  the  scientific 
value  of  all  such  theories. 

N.  T.  C. 

COLUMBUS,  Ind.,  Sept.  20,  1883. 


THE   SUN;   ITS  CONSTITUTION,  ETC. 


1. PURPOSE    OF    THIS    ESSAY DIFFI- 
CULTIES   OF    THE    SUBJECT. 


So  much  has  been  written  by 
learned  physicists  concerning  the 
central  luminary,  that  any  further 
discussion  of  the  subject,  save  upon 
the  basis  of  new~  researches,  might 
appear  either  rash  or  useless.  Yet, 
those  who  have  written  are  in  such 
irreconcilable  conflict  in  the  deduc- 
tions which  they  have  drawn  from 
observed  facts ;  while  the  results  of 
their  labors  are  in  so  many  instances 
presented  to  us  in  comparatively 
brief  essays,  or  special  lectures,  the 
sole  purposes  of  which  have  been  to 
elucidate  some  limited  feature,  or 
elaborate  some  particular  theory,  that 
a  hope  of  reconciling  inconsistencies, 
or  of  presenting  the  subject  so  as  to 
embrace  all  that  is  substantially  val- 
uable contained  in  the  many  essays 
and  lectures,  may  be  reasonably  en- 
tertained. 

If,  however,  in  pursuing  these  mod- 
est purposes  it  appear  to  be  necessa- 
ry, at  times,  to  advance  a  new  thought, 
recall  a  forgotten  fact,  or  even  pro- 
pound a  new  hypothesis;  these 
thoughts,  facts  and  hypotheses  must 
be  estimated  according  as  they  may 
be  shown  to  harmonize  with  physical 
facts  and  natural  laws. 

The  subject  will  be  treated  as  if 
nothing  had  before  been  written  upon 
it,  in  the  hope  of  being  thus  better 
understood.  While  this  method  will 
necessitate  the  repetition  of  much 
which  is  so  well  known  as  to  need  no 
such  reiteration,  yet  the  close  asso- 
ciation of  facts  well  known  with  those 
less  known  may  cause  the  latter  to  be 
more  clearly  apprehended.  Indeed, 
such  facts  as  are  universally  recog- 
nized as  truths  may  serve  as  valuable 
postulates  in  the  demonstration  of 
indispensable  hypotheses,  and  should, 
therefore,  accompany  the  enunciation 
of  the  main  proposition. 

It  should  be  borne  in  mind,  on  the 
\ery  threshold  of  this  task,  that  se- 
rious obstacles  to  the  acquisition  of  a 
direct  aud  accurate  knowledge  of  the 


subject  confront  us  at  every  point. 
Among  these,  although  not  the  most 
serious,  is  the  refractive  power  of  the 
Earth's  atmosphere,  which,  while  it 
apparently  displaces  the  Sun,  some- 
times to  a  distance  equal  to  its 
own  diameter,  thirty -three  minutes 
(33'),  may,  and  undoubtedly  does, 
distort  in  like  manner,  though  in 
less  degree,  the  relative  positions  and 
forms  of  the  details  upon  its  surface. 
An  obstacle  still  more  serious  is  the 


undulatory  and  absorptive  properties 
characteristic  of  the  Sun's  own  sur- 
roundings; for,  while  the  former 
lends  an  apparent,  and,  it  may  be, 
real  unsteadiness  to  the  object  looked 
upon,  the  latter  alters  or  changes  the 
light  which  comes  to  us,  and  causes 
it  to  produce  upon  our  admeasuring 
aud  testing  instruments  results,  the 
significance  of  which  is  yet  unknown. 
More  fatal  still  to  an  accurate  knowl- 
edge is  the  immense  distance  at  which 
the  object  must  be  examined,  and  the 
limited  powers  of  the  aiding  instru- 
ments which  man  has,  as  yet,  been 
enabled  to  bring  to  his  assistance. 

Under  such  circumstances  it  is  not 
astonishing  that  our  knowledge  of  the 
Sun  should  be  in  such  a  state  of  un- 
certainty as  must  be  disheartening  to 
all,  save  those  who,  fully  reali/ingthe 
magnitude  of  the  many  obstacles  to 
be  overcome,  entertain  feelings  of  the 
highest  satisfaction  that  so  much  has 
been  learned,  although  that  much  is 
at  the  best  but  little. 

§    2. DISTANCE    FROM    EARTH    TO    SUN. 

The  question  which  first  demands 
our  consideration  is  that  of  the  dist- 
ance of  the  Sun  from  us. 

The  laws  of  gravitation  and  the 
principles  of  geometry  suggest  to  us 
several  methods  for  measuring  this 
distance;  but,  upon  trial,  each  of 
them;  whether  because  of  disturbing 
elements  whose  values  can  only  be 
approximated,  or  because  of  unascer 
tained  details  appertaining  to  the 
heavenly  bodies,  produce  variant  re- 
sults in  all  final  calculations.  The 
third  law  of  Kepler,  that  the  square* 


THE  SUN?   ITS  CONSTITUTION,  ETC. 


3 


of  the  times  of  orbital  revolution  are 
as  the  cubes  of  the  distance  from  the 
Sun,  gives  us  only  the  relation  of  units 
of  different  denominations — time  and 
distance — without  giving  the  value  of 
these  relations  ;  and  hence  the  paral- 
laxes must  be  relied  upon  as  the  only 
means  of  obtaining  this  desired  in- 
formation. 

Yet  here  the  as  yet  unknown  value 
of  the  orbital  movement  of  the  Earth, 
in  miles,  which  is  at  the  base  of  these 
calculations,  and  can  be  approximated 
only,  will  render  any  calculation  un 
certain ;  and  different  calculations 
will  be  variant  in  proportion  to  the 
variations  of  the  approximation  made. 
A  number  of  years  ago,  a  parallax 
was  determined  from  the  planet  Mars, 
and  with  the  approximations  then 
made  an  angle  of  8.  "96  (eight  seconds 
and  ninety-six  hundredths)  was  re- 
solved upon,  which  would  make  the 
distance  of  the  Sun  nearly  96,000,000 
miles.  A  parallax  determined  at  the 
transit  of  Venus  in  1 869  was  estimated 
to  distend  an  angle  of  8."58,  making 
the  distance  95,300,000  miles.  Ob- 
servations of  the  transit  of  Yenus  in 
1874  are  calculated  to  give  a  distance 
of  93,300,000  miles. 

These  calculations,  however,  by  no 
means  establish  the  actual  distance  of 
the  Sun.  Eminent  English  astron- 
omers, Proctor  arid  Lockyer  among 
others,  from  the  same  sources  of  ob- 
servation make  different  approxima- 
tions, and  arrive  at  quite  different 
conclusions.  One  of  these  gentlemen 
makes  the  distance  92,500,000  and 
the  other  91,430,000  miles. 

Thus  a  difference  of  little  less  than 
five  millions  of  miles  in  the  computed 
distance  to  the  Sun  enters  into  our  con- 
siderations of  that  body,  with  no  data 
existing  by  the  aid  of  which  the  dis- 
crepancies can  be  removed  or  the  un- 
certainties eliminated. 

The  best  American  authorities  upon 
this  subject  have  agreed  upon  92,- 
750,000  miles  as  the  most  probable 
distance;  and  this  being  most  in  har- 
mony with  calculations  made  upon  the 
basis  of  the  supposed  velocity  of  light, 


is  the  most  satisfactory;  and  it  may 
be  considered  as  sufficiently  deter- 
mined, for  the  purposes  of  this  discus- 
sion, that  the  Sun  is  distant  from  us 
92,750,000  miles. 

§   8. THE   DIAMETER   OP   THE   SUN. 

Logically,  the  next  point  to  be  as^ 
certained  is  the  dimensions  of  that 
body.  Here,  again,  equal  uncertain- 
ties confront  us.  Since  the  micro- 
meter and  the  heliometer  have  been 
brought  into  universal  and  successful 
use,  little  difficulty  is  experienced  in 
agreeing  upon  the  angles  which  its 
disk  distends;  but  the  uncertainty 
upon  this  subject  lies  in  determining 
which  of  the  many  angles  distended 
by  it  at  different  periods  of  time  shall 
be  accepted  as  its  real  and  true  di- 
ameter. 

Owing  to  the  eccentricity  of  the 
Earth's  orbit,  there  are  periods  when 
the  Earth,  at  perihelion,  is  at  least 
3,070,538  miles  nearer  the  Sun  than 
when  farthest  away,  at  aphelion.  The 
greater  the  distance,  the  smaller  will 
appear  the  Sun's  disk,  not  only  to  the 
naked  eye,  but  to  every  measuring  in- 
strument which  may  be  applied  as 
well.  Therefore,  when  the  Earth  is  at 
perihelion,  the  disk  of  the  Sun  distends 
an  angle  of  32'  36",  while  when  at 
aphelion  it  distends  an  angle  of  only 
31'  32".  Owing  to  the  many  irregu- 
larities in  the  orbit  of  the  Earth,  pro- 
duced by  the  perturbations,  the  mean 
of  these  angles  can  only  be  approxi- 
mated. Some  astronomers  take  32'  3" 
as  the  mean  angle,  and,  assuming 
95,300,000  miles  as  the  distance  to 
the  Sun — it  is  the  distance  which  de- 
termines the  values  of  these  angles  — 
make  the  diameter  of  the  Sun  888,812 
miles.  Most  European  authors,  how- 
ever, adopt  the  lower  mean  angle  of 
32'  even,  and,  taking  91,430,200  miles 
as  the  distance,  make  its  disk  only 
852,584  miles  in  diameter. 

Most  of  our  American  astronomers 
also  adopt  32'  as  the  angle ;  but,  tak- 
ing 92,750,000  miles  as  the  distance, 
they  arrive  at  the  conclusion  that  its 
diameter  is  860,000  miles. 


THE  SUN;   ITS  CONSTITUTION,  ETC. 


Here  we  have  discrepancies  ranging 
over  a  difference  of  36,000  miles  in 
the  diameter  of  the  Sun.  What  con- 
clusions may  be  reached  from  the 
many  careful  observations  made  dur- 
ing the  transit  of  Venus  on  the  6th 
of  December,  1882,  cannot  now  be 
anticipated.  In  the  mean  time,  how- 
ever, let  the  diameter  of  the  Sun  be 
regarded  as  860,000  miles. 

§    4. THE    FORM    OF    THE    SUN. 

The  feature  next  in  order  for  con- 
sideration is  the  form  of  that  body. 
When  rising  or  setting,  and  still  close 
to  the  horizon,  the  disk,  to  the  naked 
eye,  appears  larger  at  its  horizontal 
than  at  its  perpendicular  diameter. 
At  any  marked  distance  from  the  hori- 
zon, however,  this  appearance  van- 
ishes: the  disk  presents  a  perfect 
«ircle,  and  we  are  led  to  conclude  that 
the  horizontal  appearance  was  but  an 
optical  illusion,  occasioned  by  the  re- 
fraction of  our  own  atmosphere. 
When  subjected  to  the  most  careful 
admeasurements  by  the  heliometer,  no 
differences  in  the  diameters  are  de- 
tected; this  fact  impels  to  the  conclu- 
sion that  the  disk  is  bounded  by  a  per- 
fect circle.  Upon  the  supposition, 
however,  that  the  Sun  is  a  rotating 
globe,  our  knowledge  of  the  effects  of 
centrifugal  force  would  lead  us  to  con- 
clude that  in  fact  it  had  been  oblated 
at  the  poles,  and  therefore,  that  it  is 
at  least  slightly  spheroidal  in  form. 
Yet  if  this  feature  exists,  the  oblate- 
ness  cannot  possibly  exceed  ^  parts 
of  the  equatorial  diameter,  a  quantity 
so  small  as  to  be  rendered  impercepti- 
ble by  the  intense  luminosity  of  the 
Sun's  surface. 

Although  to  the  unaided  eye  the 
Sun  presents  the  appearance  of  a  flat, 
circular  disk,  yet  when  carefully  ex- 
amined through  a  powerful  telescope, 
slight  indications  of  a  spherical  form 
are  observed.  Faint,  indeed  the 
very  faintest  possible  degradation  of 
light  near  its  limb  may  be  observed. 
True,  the  evidence  thus  obtained 
would  not,  perhaps,  by  itself  justify 
a  conclusion  of  its  rotundity  ;  yet  it 


would  be  strongly  suggestive  of  thi? 
fact,  and  prepare  the  mind  to  apply 
evidence  of  the  same  tendency  more 
readily  in  this  direction.  Upon  ap- 
plying the  thermopile  to  the  exami- 
nation, further  evidence  of  rotundity 
is  secured  in  the  disclosure  of  the  fact 
that  the  heat  rays  from  the  center — 
which  in  the  case  of  rotundity  would 
be  most  direct — are  more »:. tense  than 
those  from  near  the  margins  and  re- 
moved from  the  center,  which  in  the 
case  of  rotundity  would  also  be  more 
indirect.  Convincing  proof  of  its 
rotundity  lies  in  the  indubitable  fact 
that  it  rotates  on  an  axis. 

§  5. ROTARY   MOTION   OF   THE   SUN. 

As  has  just  been  said,  the  Sun  ie 
not  a  fixed  and  immovable  body.  On 
the  contrary,  it  is  known  to  revolve, 
or  spin  round  on  an  axis.  Proof  of 
this  is  found  in  the  observation  of 
spots  seen  upon  its  surface,  which  ap- 
pear first  on  the  eastern  side  of  the 
disk,  and  move  with  a  regular  motion 
toward  the  western  side:  there  they 
disappear,  to  reappear  after  the  lapse 
of  a  comparatively  regular  period  of 
time  on  the  eastern  limb  again,  and 
so  on,  repeating  the  same  circuit. 

Of  course  this  motion  of  the  spots 
can  be  but  seeming ;  and  the  appear- 
ance must  be  produced  by  the  actual 
movement  of  the  Sun  in  an  opposite 
direction.  Hence,  the  facts  which 
assure  us  of  the  rotary  motion  also 
inform  us  that  this  motion  is  from 
west  to  east. 

While  these  spots  furnish  satisfac- 
tory evidence  of  the  rotation,  in  a 
general  way,  the  proof  presented  by 
them  is  not  yet  understood  to  be  so 
satisfactory  as  to  the  actual  period  of 
time  occupied  by  the  Sun  in  making 
a  complete  rotation.  From  an  obser- 
vation of  these  spots  made  by  a 
Scotch  astronomer,  Prof.  Carrington, 
in  1863,  he  concluded  that  the  time 
was  24  days,  23  hours  and  19  minutes. 
Prof.  Schwabe,  in  1865,  from  similar 
observations  made  the  time  25  days 
and  five  hours.  In  1868  Pro'f. 
Sporer  arrived  at  the  conclusion  that 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


it  waa  25  days,  5  hours  and  37  min- 
utes. Later  still,  in  1871,  Prof. 
Hornstein  calculated  it  to  be  25  days 
and  13  hours.  Thus  it  is  seen  that 
even  here  we  are  confronted  with 
perplexing  uncertainties. 

In  this  instance  the  diversities  arise 
from  the  fact  of  these  spots  not  being 
stable  or  fixed  upon  the  surface  of  the 
Sun,  but  having  certain  motions  which 
are  irregular,  and  others  which  are 
supposed  to  be  separate;  and  they 
have  therefore  afforded  to  the  observ- 
er no  standard  of  time. 

The  duration  of  the  spots  is  uncer- 
tain, appearing  and  disappearing  at 
widely  different  periods  of  time.  One 
selected  for  observation  may  vanish 
under  the  eye  of  the  examiner,  and 
his  labor  upon  that  spot  be  lost.  But 
other  spots  have  been  known  to  endure 
for  quite  long  periods — in  one  instance 
for  nine  months.  If  for  such  a  period 
the  locality  of  the  spot  upon  the  sur- 
face should  remain  the  same,  it  would 
afford  sufficient  foundation  for  a  satis- 
factory deduction.  But  it  having  been 
further  observed  by  Prof.  Carrington 
that  spots  on  or  near  the  equator  move 
more  rapidly  than  spots  away  from  it 
on  any  of  the  latitudes  or  parts  of 
latitudes,  some  astronomers  have  con- 
cluded that  each  zone  of  spots,  so  to 
speak,  from  the  equator  toward  the 
poles,  revolves  in  a  different  period  of 
time,  and  that,  therefore,  this  self- 
movement  of  their  own  affords  no  re- 
liable evidence  of  the  time  in  which 
the  sun  makes  a  revolution.  The  dif- 
ference in  the  velocity  of  the  move- 
ment of  these  spots  is  said  to  be  such 
that,  while  a  spot  on  the  equator  is 
making  a  circuit  in  twenty-five  days, 
a  spot  at  30°  latitude  makes  one  in 
twenty-six  and  a-half  days. 

As  will  be  seen  hereafter,  the  calcu- 
lations based  upon  this  fact  are  mis- 
leading, and  should  have  been  elimi- 
nated from  the  elements  upon  which 
the  results  are  reached. 

§    6. PERTURBATING    MOVEMENT. 

Besides  the  rotary  motion  just  de- 
scribed, the  Sun  has  another  move- 
ment, which,  although  not  important 


in  results,  should,  however,  not  be 
overlooked.  It  is  known  that  all  the 
planets  of  the  solar  system  revolve  in 
orbits  round  the  Sun  in  different  pe- 
riods of  time.  Speaking  in  round 
numbers  only,  Uranus  makes  nearly 
two  revolutions  to  one  for  Neptune, 
Saturn  nearly  three  to  one  for  Uranus, 
Jupiter  about  two  and  a-half  to  one 
for  Saturn,  Mars  seven  to  one  for  Ju- 
piter, Earth  nearly  two  to  one  for 
Mars,  Venus  one  and  a-half  to  one  for 
Earth,  and  Mercury  more  than  two  and 
a-half  to  one  for  Venus.  It  is  there- 
fore apparent  that  times  may  arrive 
when  several,  if,  indeed,  not  all  of  these 
planets  may  be  so  nearly  in  conjunc- 
tion as  to  be  on  one  side  of  the  sun. 
In  the  event  of  such  a  concurrence, 
the  combined  attraction  of  these  sev- 
eral bodies  will  suffice  to  draw  the 
Sun  toward  them  for  a  distance  quite 
equal  to  one-half  its  disk  or  diameter. 
As  the  planets  move  on  from  this 
point  of  conjunction,  their  differing 
velocities  and  orbits  cause  them  to 
separate ;  and  as  they  become  more 
equally  distributed  around  the  Sun, 
that  body  vibrates  back  to  its  original 
locality.  This  translation  or  pertur* 
bation  of  the  Sun  is  a  movement  seL 
dom  mentioned  in  works  on  astron- 
omy, yet  it  is  one  which  the  unerring 
laws  of  gravitation  compel  us  to  recog- 
nize as  a  physical  fact,  and  our  knowl- 
edge of  that  body  would  be  incom- 
plete in  the  absence  of  this  evident 
truth. 

§  7. — THE    SUN'S     ORBITAL    MOVEMENT. 

The  Sun  has  still  another  move- 
ment which,  while  it  in  no  wise  affects 
its  present  condition,  is  yet  of  vast 
importance  with  respect  to  the  past 
history  and  future  destiny  of  that 
body,  and  all  its  attendant  satellites 
as  well.  Long  continued  observation 
of  the  starry  heavens  has  caused  the 
beholder  to  suppose  the  bright  gems 
which  besprinkle  the  firmament  to  be 
in  motion.  More  minute  examination 
proves  this  motion  to  be  apparent 
only,  accounted  for  by  either  the 
axial  or  the  orbital  motion  of  the 


THE   SUN;   ITS   CONSTITUTION,  ETC. 


Earth  5  yet  at  the  same  time  we 
learn  that  there  is  also  a  movement 
among  the  stars  which  cannot  be  ac- 
counted for  upon  the  hypothesis  of 
these  motions  of  the  Earth.  Es- 
pecially is  this  true  of  such  of  the 
stars  as  seem  to  move  continually 
along  great  circles,  which  as  yet 
have  never  been  known  to  return 
into  themselves.  Herschel  by  the 
aid  of  his,  then,  magnificent  teles- 
cope, discovered  that  in  portions  of 
tlie  heavens  the  stars  seemed  to  be 
growing  less  dense,  while  in  opposite 
portions  they  were  growing  more 
crowded,  and  that  all  appeared  to 
move  in  one  general  direction,  not- 
withstanding their  own  apparent  in- 
ternal motions.  This  general  move- 
ment appeared  to  be  from  the  Con- 
stellation Hercules,  and  toward  the 
Constellation  Argo  on  the  opposite 
side  of  the  celestial  sphere.  Assum- 
ing this  movement  to  be  apparent 
only  in  the  stars,  and  not  susceptible 
of  being  accounted  for  by  either  of 
the  two  motions  of  the  Earth  which 
have  been  named,  it  must  follow  that 
this  appearance  is  produced  by  some 
other  movement  of  the  Earth  which 
is  in  a  direction  diametrically  oppo- 
site. As  the  Earth  has  no  third 
movement,  unless  it  be  one  common 
to  all  the  bodies  of  the  system  to 
which  it  belongs,  and  inappreciable, 
for  this  reason,  it  must  be  concluded 
that  this  appearance  of  the  stars  is 
produced  by  a  contrary  movement  of 
the  entire  Solar  System.  In  such  an 
event  the  Sun  would  be  moving  to- 
ward the  Constellation  of  Hercules, 
carrying  with  it,  of  course,  all  its  at- 
tendant bodies. 

Argelander,  Struve,  Dunkin,  and 
other  astronomers  since  Herschel's 
time,  have  carefully  surveyed  this 
field  of  inquiry,  and  arrived  at  con- 
clusions strikingly  confirmatory  of 
the  views  held  by  that  Nestor  of  the 
science.  Since  then,  also,  the  spec- 
troscope has  been  brought  into  ser- 
vice, and  it  reveals  more  clearly  the 
same  fact.  Not  only  does  this  new 
worker  in  the  great  field  of  nature 


confirm  the  fact  of  this  movement  of 
the  Sun  and  its  children  through 
space,  but  it  also  teaches  us  that  it  is 
moving  in  that  direction  at  the  rate 
of  four  rniles  per  second  of  time. 

From  the  fact  that  the  Sun  and  its 
system  of  planets  seem  moving  to- 
ward a  given  point  in  the  distant 
heavens,  it  should  not  be  inferred 
that  it  is  therefore  moving  in  a 
straight  iine.  On  the  contrary,  this 
movement  must  be  supposed  to  con- 
form to  the  forward  movement  of  all 
other  heavenly  bodies,  which  in  every 
instance  is  curvilinear.  From  this 
species  of  evidence  it  is  indeed  more 
than  merely  probable  that  the  Sun 
revolves  about  the  center  of  gravity 
of  the  group  of  stars  mentioned,  of 
which  it  is  a  member,  this  center  of 
gravity  being  situate  nearly  in  the 
plane  of  the  Milky  Way,  perhaps  not 
distant  from  the  star  Rho  Herculis  to 
exceed  ninety  degrees. 

§  8. THE    SUN'S  ATTRACTIVE    FORCE 

DENSITY  OF  THE  SOLAR  MASS. 

From  what  has  been  said  it  will  be 
learned  that  in  diameter  the  Sun  is 
quite  109  times  greater  than  the 
Earth,  and  exceeds  it  in  the  mass  of 
matter  contained  355,000  times,  and  in 
the  volume  of  space  which  the  matter 
occupies  1,400,000  times.  These 
facts  being  taken  in  connection  with 
the  power  of  its  attraction  as  mani- 
fested upon  other  heavenly  bodies,  it 
is  estimated  that  the  attractive  power 
of  that  body  is  but  27  times  in  excess 
of  the  Earth's  attractive  force.  The 
matter  of  the  Sun  is  in  density  but 
one-fourth  that  of  the  Earth,  while  it 
is  1.44  times  greater  than  water. 
Using  these  results,  it  is  computed 
that  the  Sun  contains  360  quintillions 
of  cubic  miles  of  matter,  and  that  it 
weighs  two  octillions  of  tons.  It  is 
further  estimated  that  the  light  of  the 
Sun,  while  450,000  times  greater  than 
that  reflected  by  our  moon,  is  yet  one 
hundred  times  less  than  the  light 
emitted  by  the  brilliant  star  Sirius. 
The  estimated  heat  of  the  Sun  will 
be  considered  later. 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


§    9. THE    STJN'S    ATMOSPHERE. 

When  looked  upon  with  the  naked 
eye,  the  Sun  appears  as  a  huge  ball  of 
flaming  fire  ;  but  farther  than  this  the 
eye  teaches  us  nothing.  With  the  aid 
of  a  telescope,  however,  many  features 
of  the  body  and  its  surroundings  are 
developed  which  would  have  never 
been  anticipated.  Indeed,  this  vastly 
multiplied  eye  also  discloses  many 
things  of  which  it  gives  no  knowledge 
beyond  the  naked  fact  of  their  exist- 
ence, and  of  whose  details  man  would 
have  remained  entirely  ignorant  had 
not  the  spectroscope,  photograph, 
thermopile,  and  other  assisting  in- 
struments and  processes  been  discov- 
ered and  applied. 

While  these  searches  after  hidden 
truths  bring  us  much  valuable  in- 
formation, yet  all  combined  form  but 
inadequate  means  of  ascertaining  the 
nature  and  constitution  of  the  Sun. 

By  their  aid,  however,  we  learn 
that  the  body  itself  is  undoubtedly  en- 
veloped by  what  may  be  called  in  a 
general  way  an  atmosphere,  which 
extends  out  beyond  its  periphery  in 
all  directions  for  a  distance  of  200,000 
or  even  300,000  miles.  On  approach- 
ing the  sun  we  first  encounter  an  at- 
mosphere, which  is  inappreciable  on 
account  of  its  rarity  and  the  immense 
distance  at  which  it  is  viewed.  All 
along  our  path  is  found  the  omni- 
present interstellar  ether ;  but  as  we 
approach  closer  a  point  is  reached 
where  some  other  light  and  quite  im- 
ponderable gas  is  mingled  with  the 
ether.  If  the  ether  be  not  nitrogen, 
then  nitrogen,  which,  of  all  the  gases, 
is  least  subject  to  the  force  of  attrac- 
tion, and  hence  is  the  least  massed 
around  attracting  bodies,  will  be  first 
found  mingled  with  it.  At  another 
stage  of  progress  to  the  Sun,  unques 
tionably  oxygen— next  to  nitrogen  in 
the  smah  degree  of  attractive  force — 
will  be  found  mingled  with  these,  at 
first  rarely,  but  increasing  in  quantity 
with  the  approach 

At  still  another  step  on  our  advance 
evidences  of  luminosity  in  the  sur- 


rounding atmosphere  may  be  detected. 
During  a  total  eclipse  of  the  Sun  by 
the  Moon,  and  while  the  intense  light 
of  the  luminary  is  shutout  from  di- 
•ect  view,  slightly  luminous  rays  are 
seen  mingled  with  the   surroundings 
which   we  have  described.     At  first, 
only  mere   points   of  the    luminous 
matter  present  themselves,  but  as  the 
Sun   is   neared,  they   grow  broader, 
until  at  their  base,  so  to  speak,  they 
are  mingled  with  a  mass  of  luminous 
matter,  entirely  pervading  the  space 
and  surrounding  the  Sun,  in   a  form 
which  in  its  general  aspects   may  be 
said  to  be  spherical.    At  times,  these 
projections   are  seen   to   extend  out- 
ward beyond  the  mass  of  the   lumin- 
ous surrounding  for  distances  ranging" 
from   one  to  two   hundred   thousand 
miles.     These  rays  or  projections  are 
pinkish     in   color,   and    are  not  in- 
variably  in   the    direct    line  of  the 
radii   of  the   Sun,   but   at    different 
places  and  times  have   now   a  tan- 
gential direction;  again,  a  curved  one. 
Whether  the  atmosphere  proper,  into 
which    they     are    projected,    is    in 
motion,  as    is    sometimes  our   own, 
whether  it  serves  as  an   irregular  re- 
tarding   medium,    or    whether  both 
these  conditions  combine  to  produce 
these  features  cannot  be  satisfactorily 
settled.     While  this   luminosity  was 
first  discovered  during  an   eclipse   of 
the   Sun,  yet  later,  both   Janssen  of 
Paris,  and  Lockyer  of  London,  were 
enabled  to  detect  its  presence  at  any 
time  when  our  own  atmosphere   was 
quiet,  by  the  aid  of  the  spectroscope. 
These  protuberances  have  been  sub- 
jected to  spectroscopic   analysis,  but 
without    entirely  conclusive    results. 
These  efforts,  however,  disclose  a  faint 
continuous   spectrum,   in   which  the 
dark  lines  of  the  solar  spectrum  are 
discernible,  indicating  a  reflected  sun- 
light.    This  evidence  also  assures  us 
that  they  are   in   part,  at  least,  com- 
posed of  gases,  which,   while  lumin- 
ous, are  not  in  such  a  highly  heated 
state   as    to   be    self-luminous.     The 
dark  lines   of  the  spectrum  teach  us 
that  the  light,  before  reaching  our  at- 


THE  SUN;   ITS  CONSTITUTION,  ETC. 


mosphere,  passes  through  or  among 
incandescent  gases  which  have  culled 
out  some  of  the  light  vibrations  of 
the  body  emitting  them.  This  spec- 
trum is,  therefore,  silent  but  impres- 
sive proof  that  the  projections  are, 
indeed,  thrown  out  into  a  gaseous  at- 
mosphere not  wholly  unlike  our  own. 

Lockyer  unhesitatingly  pronounces 
other  portions  of  this  spectrum  to  be 
dncontestible  evidence  of  burning  or 
glowing  hydrogen  —  a  substance 
which,  as  all  physical  astronomers  ad- 
mit, predominates  in  the  mass  of  lu- 
minous matter  nearer  the  Sun  Prof. 
Young  also  holds  these  projections  to 
be  hydrogen  flames. 

There  is  still  another  feature  of 
this  spectrum  which  must  not  be  for- 
'gotten.  It  is  a  single  bright  line  in 
the  green  portion,  which  has  not  been 
identified  as  the  spectrum  of  any 
known  substance.  Whether  this  in- 
dicates the  presence  of  some  substance 
not  yet  known  and  named,  or  of  some 
known  substance  placed  in  a  condi- 
tion unknown  to  us  is  uncertain,  as 
man  is  as  yet  learning  only  the  alpha 
Jbet  of  the  langauge  of  the  spectrum. 

Unfortunately,  nearly  all  authors 
treat  of  these  projections  as  if  they 
'were  poi  tions  of  matter  distinct  and 
different  from  that  found  nearer  or 
farther  from  the  Sun.  They  are 
given  a  name — Corona — which  is 
calculated  to  confuse,  if  not  actually 
mislead  ;  but  it  should  ever  be  borne 
in  mind  that  they  are  but  portions  of 
the  more  interior  surroundings  of 
the  Sun  projected  through  this 
atmospheric  surrounding  by  some 
force  within  or  beneath  it  Mr. 
Lockyer,  the  eminent  English  spectro 
scopist,  with  the  hope  of  making  the 
subject  clear  to  all,  says  the  Sun  is 
immediately  surrounded  by  an  atmos- 
phere composed  principally  of  hydro- 
gen gas,  portions  of  which  are  here 
and  there  thrown  out  beyond  the 
general  mass  in  the  form  of  enormous 
hydrogen  flames. 

§  10. — THE    CHROMOSPHERE. 

As  has  just  been  incidentally  men- 


tioned, after  another  stage  of  advance 
upon  the  Sun,  following  inward 
on  the  line  of  these  projections, 
we  find  that  the  luminous  matter 
first  observed  in  distinct  parts,  has 
become  general  throughout  the  space 
surrounding  the  body,  and  that  this 
entire  stratum  of  atmosphere  is  ren- 
dered luminous.  The  region  of  space 
between  the  point  where  the  luminos- 
ity becomes  general  and  the  surface 
of  the  Sun,  from  the  fact  of  its  pos- 
sessing color  (chrome),  is  named  the 
Chromosphere. 

This  portion  of  the  Sun's  covering 
is  variously  estimated,  at  from  one  to 
two  hundred  thousand  rniles  in  depth, 
not  accurately  uniform  in  shape,  but 
growing  constantly  more  dense  as 
the  Sun  is  approached. 

With  the  telescope  no  differences 
are  observed  between  the  Corona- 
projections,  and  the  Chromosphere, 
save  in  the  mere  form.  Within  this 
chromosphere,  as  a  pirt  of  it,  may  be 
seen  by  the  telescope  during  eclipses, 
or  detected  by  the  spectroscope  at 
almost  any  time,  projecting  outward- 
ly from  the  surface  of  the  Sun,  cer- 
tain prominences,  distinguishable  in 
color,  density,  and  intensity,  from  the 
general  mass  of  luminous  matter  in 
which  they  appear.  When  seen  they 
are  invariably  noticed  to  be  at,  or 
near  the  equatorial  regions  of  the 
Sun,  and  always  in  the  line  of  the 
projections  which  have  been  named 
the  Corona.  Mr.  Swift,  who  ob 
served  the  eclipse  of  1878  from  Capi- 
tol Hill,  Denver,  saw  two  of  these 
prominences,  which  he  describes  as  be- 
ing near  the  chromospherical  crescent 
(from  the  drawing  accompanying  his 
description,  it  must  be  understood 
that  he  means  by  this,  the  edge  of  the 
Chromosphere  nearest  the  Sun)  pos- 
sessing the  same  general  tint — a 
bright  pink — located  each  in  the  line 
of  immense  projections  beyond  the 
Chromosphere.  Their  spectrum  con- 
sists chiefly  of  bright  lines  on  a  dark 
ground,  several  of  which  are  coinci- 
dent with  the  known  lines  of  glow- 
ing hydrogen.  A  spectrum  analysis 


THE  SUN;  ITS   CONSTITUTION,  ETC. 


of  the  entire  Chromosphere,  shows 
us  that  its  outer  portion  is  largely 
hydrogen,  while  in  the  portions  nearer 
the  Sun,  iron,  magnesium,  oxygen, 
nickel,  sodium,  and  many  other  sub- 
stances known  to  us,  are  discovered. 
Thus  their  spectra  compel  us  to  con 
elude,  that  these  prominences  are  of 
the  same  nature  and  character  as  the 
surrounding  Chromosphere. 

§      11.— OOBONA,      PROMINENCES,      AND 
FACULJE. 

A  critical  review  of  all  that  has 
been  learned  of  these  so-called  prom- 
inences, leaves  no  reasonable  doubt 
that  they  differ  in  no  respect,  except 
in  extent,  from  the  phenomena  which 
have  long  been  observed  on  the  mar- 
gins of  many  solar  spots,  and  given 
the  name  of  faculae.  On  the  edges 
of  some  of  these  spots  are  seen  ele- 
vated ridges  of  a  lighter  color,  and 
brighter  than  the  general  surface  of 
the  Sun.  As  early  as  1859,  the  En- 
glish astronomer,  Dawes,  proved  by 
observation  that  when  viewed 
obliquely,  as  at  the  limb  of  the  Sun, 
these  faculas  rose  in  elevated  ridges 
far  above  the  general  level.  In  1862, 
Prof.  Hewlett  observed  an  appear- 
ance which  renders  the  connection 
between  the  faculse  and  these  promi- 
nences quite  certain .  Just  as  a  large 
spot  was  passing  off  the  Sun's  disk, 
he  saw,  on  either  side  of  the  nucleus, 
these  faculae  thrown  up  far  above  the 
Sun's  surface,  like  mountain  ridges  or 
peaks.  Father  Secchi,  of  Rome,  re- 
moves any  lingering  doubt  upon  this 
question.  He  says  :  "  When  a  spot 
is  on  the  Sun's  border  during  its  first 
period,  although  the  dark  region  (nu- 
cleus) is  not  visible,  its  position  is  in- 
dicated by  eruptions  of  metallic  va- 
pors."* This  important  discovery  is 
confivmed  by  the  observations  of 
Prof.  Young,  who  says :  "  It  is  cer- 
tain that  very  commonly,  if  not  in- 
variably, there  is  a  violent  uprush  of 
hydrogen  and  metallic  vapors  all 
around  the  outer  edge  of  the  penum- 
bra1' of  the  spots. 

Newcomb's  Astronomy,  p.  276. 


It  being  thus  admitted  by  these 
learned  scientists,  that  the  .spots  are 
accompanied  with  an  eruptive  foroe — 
and  in  fact  no  one  can  doubt  it — 
philosophy  requires  us  to  assume  that 
this  power  is  commensurate  witlrthe 
magnitude  of  all  things  with  which 
it»  is  associated.  With  a  powef  of 
such  immensity,  it  would  not  be  sur- 
prising to  find  it  projecting  the  light- 
est of  the  erupted  gases  to  a  distance 
of  many  miles — miles  at  least  equal 
to  one-quarter  of  the  diameter  of  the 
body  from  which  they  are  projected 
— to  the  uttermost  extremities  of  the 
Corona.  The  known  appearances  of 
the  faculse  are  precisely  similar  to 
those  known  of  the  prominences,  oc- 
cupy the  same  relative  positions 
upon  the ,  Sun,  are  in  line  with  the 
radii  of  the  circle,  and  the  promi- 
nences are  invariably  at  the  base  of 
the  marked  projections  of  the  Corona, 
while  the  spectra  of  all  are  the 
same. 

The  physical  fact  that  these  projec- 
tions are  greatest  in  extent  in  the 
direction  of  the  polai  region  affords 
no  objection  to  this  conclusion.  It 
must  be  remembered  that  much  the 
larger  proportion  of  these  eruptive 
spots  lie  on  either  side  of  the  Equa- 
tor, and  near  thereto ;  and  as  the 
eruptions  are  in  line  of  the  radii,  the 
projections  would,  and  as  a  matter  of 
necessity  must  be,  mostly  in  a  direc- 
tion poleward.  This  would  cause  the 
Corona  to  be  and  appear  more  nearly 
a  cuboid  than  a  spheroid 

While  it  is  within  the  range  of  a 
reasonable  probability  that  all  the 
luminous  matter  of  the  Corona,  and 
much  of  the  luminous  matter  of  the 
Chromosphere  is  thrown  into  space  by 
the  eruptive  process  from  these  spots, 
yet  it  does  not  follow  that  all  the 
luminous  matter  of  the  latter  is  placed 
in  its  locality,  in  this  manner.  Upon 
any  possible  hypothesis  concerning 
the  body  of  the  Sun,  which  admits  it 
to  be  in  a  highly-heated  state— 
whether  the  matter  be  in  a  vapor, 
cloud,  or  fluid  condition — there  will 
be  continuouslv  emitted  from  thesur^ 


10 


THE  SUN; 'ITS  CONSTITUTION,  ETC. 


face,  at  all  points,  in  every  direction, 
with  comparatively  equal  force,  atoms 
of  heated  gases  precisely  as  they  are 
seen  to  escape  from  the  surface  of 
any  terrestrial  body  when  highly 
heated.  These  particles,  or  atoms, 
united  with  those  erupted,  suffice  to 
form  the  Chromosphere. 


§  12.- 


CHE    PHOTOSPHERE. 


Within  the  center  of  this  Chromo- 
sphere is  seen  the  disk  or  body  of  the 
Sun.  This  even  and  comparatively 
unchanging  surface  is  by  astronomers 
and  physicists  styled  the  Photosphere 
— meaning  the  sphere  of  light.  Of 
this  sphere  the  unaided  eye  teaches 
us  nothing  beyond  its  mere  existence 
in  a  heated  and  luminous  condition. 
With  the  aid  of  a  telescope  of  suffi- 
cient magnifying  power  to  apparently 
bring  the  body  within  200,000  miles 
of  us,  the  details  of  this  surface  may, 
to  a  slight  extent,  be  studied.  Under 
such  an  examination  it  will  be  seen 
to  present  a  mottled  appearance, 
Comparable  to  that  of  very  light  and 
-ieecy  clouds.  The  outlines  of  these 
fjloud-like  masses  are  indistinct,  and 
seem  subject  to  constant  changes. 
The  same  portions  will  differ  at  differ- 
ent times  in  general  appearance  to 
the  same  eye,  while  different  impres- 
sions are  made  upon  different  visions. 
Hence  the  diversities  in  the  descrip- 
tions given  by  different  observers. 

Nayemith,  of  England,  examining 
with  the  best  of  instruments,  says 
the  appearance  presented  to  him  was 
not  unlike  that  which  would  be  pro- 
duced by  the  interlacing  of  long,  nar- 
row objects,  which,  running  andcros 
sing  in  all  directions,  form  a  net- 
work of  interwoven  willow  leaves. 
Prof.  Newcomb  says  it  presents  to 
him  the  appearance  of  a  fluid  in 
which  rioe  grains  are  held  suspended. 
To  others,  it  presents  such  an  appear- 
ance as  might  be  produced  by  a  body 
of  red-hot  iron,  at  such  a  distance 
that  the  heat  waves  and  escaping 
gases,  coming  from  it  in  every  pos- 
sible direction  and  with  every  degree 
of  velocity,  seemed  to  constitute  a 


part  of  the  body  itself.  This  uncer- 
tainty renders  a  study  of  its  telescopic 
appearance  quite  profitless. 

The  only  physical  fact  learned  re- 
garding the  Sun's  surface  by  the  as 
sistance  of  the  telescope  is,  that  at  or 
near  its  equatorial  regions,  are  fre- 
quently seen,  here  and  there,  compar- 
atively small  patches  or  spots,  whose 
centers  are  quite  dark  in  appearance, 
and  whose  outer  rims,  while  less  so. 
are  yet  darker  than  the  surrounding 
surface  of  the  Sun.  These  spots  are 
found  not  to  be  stable  in  endurance, 
but  to  come  and  go,  each  independent 
of  the  others  ;  all  of  which  details 
will  be  more  fully  developed  as  we 
proceed. 

The  spectrum  of  the  surface  is  seen 
to  be  continuous,  giving  evidence  of 
matter  in  such  a  condition  that  its 
constituent  parts  are  in  contact,  as  in 
the  case  of  solids  or  fluids,  but 
excluding  the  condition  of  free  gases. 
The  further  details  of  this  surface 
can  be  learned  only  in  studying  the 
condition  of  the  matter  competing  iu 

§  13. — THE    SUN'S    HEAT. 

The  most  ordinary  experience 
teaches  us  that  the  sun  is  a  source  of 
heat,  and  since  in  this  day  it  is  not 
contended  that  the  heat  lies  in  its  at- 
mosphere, it  must  be  conceded  that 
the  body  itself  is  in  a  heated  state. 
By  applying  the  common  focus  lens 
we  are  admonished  that  it  is,  indeed, 
intensely  hot,  but  this  instrument 
does  not  register  the  degrees  of  tem- 
perature there  attained.  To  deter- 
mine a  mode  of  measuring  these  de- 
grees man  has  striven  for  years.  Sir 
Isaac  Newton  devoted  much  atten- 
tion to  this  subject,  and  finally  form- 
ulated what  was  long  supposed  to  be 
a  law  of  radiation,  by  which  the 
effective  temperature  of  the  Sun  could 
be  correctly  registered  in  degrees  of 
the  thermometer.  This  law  was  based 
upon  an  assumed  proportionality  be- 
tween the  heat  radiated  and  the  tem- 
perature of  the  radiating  mass,  which 
had  been  deduced  from  artificial 
heat.  It  has  since  been  ascertained 


THE   SUN;  ITS   CONSTITUTION,  ETC. 


1? 


that  this  basis  is  erroneous  when  ap- 
plied to  the  Sun,  giving  the  degree  of 
heat  in  that  body  as  being  much 
higher  than  it  could  possibly  be. 

Since  Newton's  time  other  theories 
of  radiation  have  been  conceived 
which  have  been  made  to  conform  to 
the  more  accurate  knowledge  ac- 
quired and  more  perfect  instruments 
applied.  But  the  results  of  different 
experiments  are  so  variant  that  no 
certainty  can  be  attained.  Pouillet, 
Deville  and  Rosetti  differ  in  their 
estimates  widely,  giving  respectively 
3,000°,  10,000°  and  18,000°  Fahr.  as 
the  effective  heat  of  the  Photosphere. 
The  method  adopted  by  Rosetti  is 
the  most  satisfactory  to  many  learned 
men,  while  others  regard  his  estimate 
as  entirely  too  high.  It  is  possible 
that  in  the  future  the  spectrum  of  the 
Sun-surface  will  be  so  read  as  to  ac- 
quaint us  with  the  true  state  of  the 
temperature;  in  the  mean  time,  since 
all  other  methods  are  unreliable,  we 
are  left  to  what  inferences  may  be 
drawn  from  such  manifestations  or 
phenomena  of  the  Sun  as  give  evi- 
dence of  the  condition  or  state  of 
matter  found  there. 

At  the  temperature  given  by  Ro- 
setti the  most  refractory  substances 
known  to  us,  even  platinum,  fire-clay, 
and  the  diamond  itself,  would  be  re- 
duced to  a  molten  state,  while  most 
others  would  be  dissipated  in  vapor 
or  gas  but  for  several  philosophical 
reasons,  which  will  be  developed  in 
the  further  examination  of  this  sub- 
ject. 

§    14. CONDITION    OF   THE   INTERIOR. 

Prof.  Young,  of  Princeton  College, 
one  of  the  best  authorities  upon  this 
subject,  says :  "  The  temperature  of 
different  portions  of  the  solar  envel- 
ope (Photosphere),  must  vary  enor- 
mously, increasing  as  we  descend 
below  the  surface,  so  that  in  all 
probability  there  may  be  a  difference 
of  thousands  of  d agrees  between  the 
temperature  at  the  upper  surface  of 
the  Photosphere  and  that  at  the  Sun's 
center,  or  even  at  the  depth  of  a  few 


thousand  miles."*  Prof.  Newcombr 
in  speaking  upon  this  subjeet,  says : 
"  For  the  temperature  of  the  Photo- 
sphere, it  seems  likely  that  the  lower 
estimates  are  more  nearly  right,  being 
founded  on  experimental  law,  but  the 
temperature  of  the  interior  must  be 
immensely  higher/'  Again,  he  says: 
"  The  be^t  sustained  theory  of  the  in- 
terior is  the  startling  one  that  it  is 
neither  solid  nor  liquid,  but  gaseous ; 
so  that  our  great  luminary  is  nothing 
more  than  a  mere  bubble."  Indeed 
all  who  of  late  years  have  given  this 
subject  due  consideration  concur  in 
the  conclusion  that  the  interior  of  the 
Sun  is  heated  several  thousand  de- 
grees higher  than  the  surface. 

§  15. EFFECTS  OF  HEAT  ON  MATTER. 

A  knowledge  of  the  effects  which 
heat  has  upon  matter,  assures  us  that 
a  temperature  so  high  as  that  which 
must  prevail  in  the  interior  of  the 
Sun,  is  sufficient  to  reduce  all  matter 
affected  by  it  to  a  gaseous  state ;  but 
as  the  process  by  which  this  result  on 
matter  is  secured,  is  so  imperfectly 
understood  or  generally  forgotten  as 
to  lead  to  important  errors  in  assign- 
ing this  gaseous  matter  its  proper 
office  in  the  production  of  other  ma- 
terial manifestations  in  the  Sun,  it 
will  be  briefly  stated. 

The  phenomenon  of  matter  which 
is  called  temperature,  caloric  and 
heat,  is  but  a  status  of  that  matter 
in  which  its  atoms  or  molecules,  or 
both,  are,  as  among  themselves,  in 
commotion  more  or  less  active.  The 
greater  the  activity  of  this  commotion, 
the  higher  is  said  to  be  the  degree  of 
heat.  Now,  space  is  an  essential 
condition  of  this  commotion  among 
the  molecules  or  atoms.  In  dense 
matter,  one  atom  or  molecule,  to 
make  this  motion,  presses  against  a 
neighboring  atom  or  molecule,  and 
to  the  extent  of  "Its  >power  displaces 
the  obstructing  neighbor,  which  in 
turn  displaces  its  neighbor,  and  in 
this  manner  the  commotion  is  spread 


*  Popular  Science  Monthly,  Nov.,  1880. 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


throughout  the  mass  of  matter.  This 
commotion,  like  all  other  results  from 
natural  forces,  is  commensurate  with 
the  cause.  If  the  cause  be  great  and 
persistent,  the  commotion  will  be  ac- 
tive and  powerful.  As  the  commo- 
tion is  increased  in  these  particulars, 
the  pressure  for  room  between  the 
constituent  particles  rises  to  a  degree 
of  violence,  which  may  be  called  con- 
cussion. These  concussions  increase 
through  the  active  force  producing 
them,  in  number,  frequency  and 
power,  and  the  distance  between  one 
molecule  or  one  atom  and  another  is 
correspondingly  increased,  the  de- 
gree of  separation  being,  of  course, 
dependent  upon  the  extent  of  the 
force  which  produces  the  commotion. 
If  the  degree  of  separation  produced 
is  but  partial,  the  matter  is  said  to  be 
in  a  fluid  state,  while,  if  the  separa- 
tion produced  is  complete  and  abso- 
lute, the  matter  is  said  to  be  in  a 
gaseous  condition.  Thus,  when  it  is 
said  that  the  matter  constituting  the 
interior  of  the  Sun  is  in  a  gaseous  state, 
it  will  bo  understood  that  such  a  com- 
motion has  been  excited  and  main- 
tained among  the  constituent  parti- 
cles of  the  matter,  as  to  drive  them 
BO  completely  asunder,  that  all  at- 
traction of  cohesion  or  adhesion  be- 
tween them  has  been  destroyed  and 
they  are  left  free  to  move  independ- 
ent of  their  former  associations  or 
connections.  It  may,  therefore,  be 
correctly  concluded,  that  while  the 
higher  degree  of  heat  in  the  interior 
may  be  sufficient  to  reduce  matter  to 
a  gaseous  state,  the  less  degree  of 
heat  at  the  Photosphere  may  be  suf- 
ficient only  to  reduce  it  to  a  fluid  con- 
dition. 

§  16. TUB   EXPANSIVE   POWER    OF 

HEAT. 

The  description  of  heat  just  given 
brings  us  to  the  consideration  of 
another  feature  of  its  effects  upon 
matter.  The  separation  of  the  con- 
stituent particles  causes  them  to  oc- 
cupy more  space  as  a  whole  than 
when  in  quiet  contact  as  a  solid. 


That  all  solids  expand  and  increase  in 
size  under  the  influence  of  this  force 
is  a  fact  too  well  known  to  need 
proof.  The  extent  to  which  this  ex- 
pansion may.be  carried,  even  in  me- 
chanics, is  shown  to  be  comparatively 
limitless.  The  force  or  power  which 
accompanies  this  expansion  is  beyond 
our  comprehension,  even  when  excited 
by  the  very  limited  causes  at  the 
command  of  man.  The  power  of  an 
expanding  iron  bar  is  vastly  in  excess 
of  the  fire  which  produces  it ;  the  ex- 
pansive power  of  steam  can  be  made 
to  excel  any  resistance  which  may  be 
applied  against  it,  while  the  irresisti- 
ble force  of  burning  gunpowder  is  but 
the  expansive  power  of  heated  air. 

Whoever  recalls  these  well-known 
effects  of  heat  upon  matter,  and  re- 
members that  this  expansion  and  its 
irresistible  power  are  inseparable 
results  of  commotion  among  the 
molecules  or  atoms  of  matter,  can 
certainly  not  fail  to  appreciate  that 
while  the  matter  composing  the  in- 
terior of  the  Sun  is  being  reduced  to 
this  gaseous  condition,  it  is  being  ex- 
panded, and  tljat  this  expansion  is  ;i 
force  commensurate  with  the  cause 
which  put  the  atoms  in  such  commo- 
tion as  to  impel  their  separation. 
Yet  it  is  remarkable  that  this  expan- 
sive force — which  universally  accom- 
panies the  reduction  of  matter  by 
heat — has  been  overlooked  by  even 
the  most  learned  and  careful  of 
scholars  when  treating  of  the  Sun  and 
its  phenomena.  The  importance  of 
this  element  will  be  developed  as  we 
proceed. 

As  this  expansive  power  in  terres- 
tial  matter  will  prevail  over  all  infe- 
rior force  which  may  attempt  to  re- 
tard or  resist  it;  so  the  expansive 
force  accompanying  the  reduction  of 
matter  to  a  state  of  gas  in  the  inte- 
rior of  the  Sun  would  prevail  over 
any  or  all  inferior  forces  which  rai^ht 
serve  as  a  hindrance  or  retarding 
element.  If  no  retarding  forces  were 
arrayed  against  it,  the  atoms  or 
molecules  would  assume  their  sepa- 
rate distances,  and  occupy  increased 


THE  SUN;  ITS   CONSTITUTION,  ETC. 


13 


space  without  violence,  while  if,  from 
any  source,  a  hindering  force  to  this 
expansion  was  presented,  the  in- 
creased space  would  be  secured  with 
a  violence  necessary  to  overcome  the 
opposing  force.  As  the  two  contend- 
ing forces — expansion  and  resistance 
—increased  in  power,  the  violence 
with  which  the  victory  is  finally  won 
by  the  former,  might  increase  in  in- 
tensity until  that  grade  is  reached, 
which  is  designated  by  the  term  ex- 
plosion. The  question  naturally  pre- 
sents itself  here:  Is  there  any  re- 
sistive force  presented  to  the  expan- 
sive power  of  the  matter  being  re- 
duced in  the  interior  of  the  Sun? 
Let  us  see  whether  this  question  can 
be  satisfactorily  answered. 

§    17. THE    SUN'S    CKUST. 

Since  it  is  now  quite  universally 
conceded  by  the  learned,  that  the 
supply  of  heat  in  the  Sun  is  mainly 
— if  not  wholly — maintained  by  the 
molecular  disturbances  produced  by 
the  constant  contraction  of  a  crust, 
which  has  condensed  over  the  more 
interior  portion  of  the"  Sun,  an  argu- 
ment to  prove  the  existence  of  such 
a  crust  might  seem  quite  unnecessary. 
Yet  in  considering  so  important  a 
matter  as  the  condition  of  the  Sun, 
nothing  should  be  assumed,  and 
everything  be  proven. 

It  were  impossible  to  determine, 
by  philosophy,  the  existence  of  the 
crust  without  considering  the  causes 
which  produce  it.  Therefore,  let  us 
ascertain  whether  there  are  present 
in  or  about  the  Sun,  such  causes  or 
forces,  as  would  cause  a  crust  to  form 
or  remain  over  the  interior  of  the  Sun. 

In  the  very  nature  of  matter  and 
its  forces  there  must  be  a  far  less  de- 
gree of  heat  in  the  atmosphere  sur- 
rounding than  in  the  body  of  the  Sun. 
The  correctness  of  this  conclusion 
will  be  apparent  when  another  study 
of  the  phenomenon  of  heat  is  made. 
It  is  evident  that  when  the  commotion 
among  atoms  and  molecules  has  so 
completely  separated  them,  that  they 
are  diffused  into  free  gases,  that  is  to 


say,  into  their  atomic  condition,  the 
spaces  between  the  atoms  are  too 
great  to  permit  further  concussions 
and  rebounds.  The  instant  they 
cease  to  come  thus  in  contact,  that  in- 
stant the  commotion  between  them 
begins  to  decline  in  activity,  and  the 
atoms  ultimately  relapse  into  a  state 
of  comparative  quietude.  This  dif- 
fusion into  space  is  a  "  cooling"  pro- 
cess, the  degree  of  heat  decreasing 
with  an  increased  degree  of  expansion. 
Therefore,  it  is  universally  true  of 
atmospheric  gases  that  they  are,  in 
and  of  themselves,  incapable  of  en- 
gendering, or  of  long  maintaining,  a 
heated  condition,  and  must  become 
cold. 

It  will,  however,  not  be  overlooked 
that  atmospheric  gases  immediately 
surrounding,andin  contact  with  incan- 
descent bodies,  cannot  relapse  into  a 
condition  of  absolute  coldness,  for  the 
reason  that  the  commotion  amongthe 
atoms  of  the  body  will  be  communi- 
cated by  conduction — not  radiation— 
to  the  atmospheric  atoms  in  contact, 
which  commotion  these  in  turn  will 
communicate  by  conduction  from  ac- 
tual contacts,  or  by  the  interstellar 
ether  always  in  contact,  to  neighbor- 
ing atoms  more  remote  from  the  in- 
candescent center,  until  the  effect  is 
finally  lost  in  repetitions  or  from 
other  causes.  Still,  the  very  diffused 
condition  of  the  atoms  thus  affected 
precludes  the  possibility  of  their  com- 
motion ever  becoming  exceedingly 
active;  hence,  they  must  necessarily 
be  in  degree  of  heat  immensely 
below  that  of  the  body  which  they 
surround — a  degree  of  heat  BO  low 
that  it  may  be  designated  as  a  condi- 
tion of  comparative  coldness. 

The  coldness  of  this  surrounding 
atmosphere  produces  upon  the  in- 
candescent surface  of  the  body  re- 
sults in  turn  which  demand  our  con 
sideration.  The  atmospheric  atoms 
in  a  state  of  quietude  are  in  contact 
with  the  photospheric  atoms  in  a 
state  of  commotion.  While  the  com- 
motion of  the  latter  would  be  slightly 
communicated  to  the  former,  as  has 


14 


THE  SUN;   ITS   CONSTITUTION,  ETC. 


just  been  described,  it  also   follows 
that  the  inertia  of  the   atmospheric 
atoms  would  serve  as  a  resistive  force 
to  the  commotion  in  the  body,  and,  to 
the  extent  of  this  inertia,  would  put  the 
atoms  of  the  body  in  a  state  of  quie 
tude.   The  proficiency  of  this  quieting 
force  will  be  greater  as  the  pressure 
of  the  atmospheric  atoms  againstthe 
others  are  increased.     This  pressure 
will  be  most  powerful  in  case  metal- 
lic gases — which  are  strongly  attrac 
tive — largely  permeate  the  surround 
ing  space. 

Thus  the  laws  of  natural  forces — 
and  they  are  the  same  everywhere — 
require  us  to  hold  that  matter  at  the 
surface  of  the  body  in  contact  with 
the  cold  strata  of  the  surrounding 
atmosphere,  must  be  in  a  state  of 
quietude,  compared  with  interior 
atoms,  not  subject  to  this  influence. 
Yet  it  will  not  be  understood  that 
the  surface  atoms  only  are  thus  af- 
fected, but  that  the  result  will  follow 
inwardly  as  the  commotion  of  each 
stratum  of  interior  atoms  is  lessened 
by  the  communicated  retarding  in- 
fluence, which  lessens  as  it  proceeds, 
and  is  finally  lost  in  the  presence  of 
a  greater  disturbing  influence.  The 
consequences  of  such  a  condition  of 
things  should  now  be  examined. 

As  has  been  seen,  the  commotion 
among  atoms  or  molecules  acts  as  a 
repulsive  force  and  separates  the 
atoms.  Attraction  is  a  concentrat- 
ing force,  and  would  bring  atoms  into 
close  contact.  They  are,  therefore, 
conflicting  forces,  the  inferior  of  which 
will  be  overcome  by  the  superior. 
The  repulsive  force  is  a  created 
one,  which  ebbs  and  flows  with  the 
cause  that  gives  it  birth,  while  the 
attractive  force  is  inherent  in  matter, 
and  is  ever  present,  ever  equally  ac- 
tive, although  it  may  be  rendered  less 
effective,  and,  indeed,  entirely  over- 
come by  a  superior  force.  It  follows 
then,  that  the  effectiveness  of  the  at- 
tractive force  is  in  an  inverse  ratio 
to  the  repulsive  power. 

At  the  surface  of  the  body,  and  it 
matters  not  whether  the  body  be  a 


mere  vapor,  cloud,  fluid  or  solid,  the 
commotion  among  its  constituent 
j> articles  must  be  slight  when  under 
the  influence  of  such  retarding  and 
resisting  influences,  in  which  case  the 
attractive  force  must  be  effective,  and 
succeed  in  drawing  the  atoms  into 
close  contact,  producing  greater  con- 
densation as  it  proceeds.  Density  of 
matter  is  the  result  of  attraction  and 
attraction  only. 

An  irresistable  conclusion  from 
these  premises,  is  that  the  matter  at 
the  surface  of  the  Sun,  where  the 
attractive  force  is  effective,  must  be 
and  is  more  dense  than  in  the  inte- 
rior where  the  commotion,  called  heat, 
has  engendered  an  overpowering  re- 
pulsive force.  How  deep  into  the 
interior  of  the  mass,  these  condensing 
powers  may  in  the  course  of  time 
succeed  in  overcoming  the  expansive 
force  can  be  judged  only  from  effects 
and  results  hereafter  to  be  observed. 
This  condensed  portion  of  the  mass 
is  designated  by  the  different  names 
of  "shell"  and  "crust,"  and,  as  has 
been  remarked,  is  recognized  by  all 
modern  writers  upon  this  subject,  al- 
though most  of  them  have  invented 
processes  for  its  formation  which  are 
hardly  in  accord  with  the  principles 
of  natural  philosophy,  chemistry  and 
mechanics. 

Such  a  crust  of  matter  on  the  ex- 
terior of  the  Sun  would  afford  a  re- 
sistance to  the  passage  of  atoms  of 
matter  through  it,  as  well  as  to  the 
expansion  of  matter  interior  to  itself 
directly  proportionate  to  the  density 
of  this  crust.  Physicists  differ  widely 
n  their  conclusions  as  to  this  density, 
holding  either : 

1.  That  it  is  gaseous  and  under  in- 
tense pressure  ; 

2.  That  it  is  highly  vaporous — in 
density  between  gases  and  fluids  ; 

3.  That  it  is  cloud-like — a  state  of 
density  between  a  vapor  and  fluid ; 
or, 

4.  That  it  is  a  fluid. 

§    18. THE    GASEOUS    THEORY. 

There  are  but  few  scientists  at  this 


THE  SUN ;  ITS  CONSTITUTION,  ETC. 


15 


day  who  insist  upon  the  gas  theory. 
Yet  some  who  are  eminent  maintain 
that  the   shiny    appearance   of    the 
photosphere  is  produced  by  the  heavy 
pressure  of   the  superincumbent  at- 
mosphere upon  gaseous  matter,  and 
not    by  its  own   incandescence.     It 
has,  however,    been  well  established 
that  the  photosphere  is  self-luminous, 
and  would  shine  in  any  state  or  con- 
dition.    The  gaseous  theory  is  based 
upon  the  proposition  that  the  surroud- 
ing  atmosphere  rests  upon  the  photo- 
sphere with  great  pressure,  a  proposi- 
tion which  is  antagonistic  to  every 
known  natural  law  governing  matter 
in  a  highly  heated  condition.     There 
is  no  cause,  save   attraction,  which 
can  produce  a  pressure  of  matter  in 
nature,  and  attraction  would  be  less 
powerful  in  the  free  gases  of  the  sur- 
rounding atmosphere  in  a  somewhat 
heated  state  than  in  the  more  con- 
densed  matter  of    the   photosphere. 
Indeed,  as  attraction  is  weak  in  the 
gases  of  the  Earth's  atmosphere — com- 
paratively unheated — and  creates  too 
slight  a  pressure  upon  matter  here  to 
produce  any  visible  effects,  so  must  it 
be   even   in   a  much  greater  degree 
with  the  Sun  whose  chromosphere  is 
highly  heated.    Beside  this  considera- 
tion, there  is  another  which  is  quite 
as   conclusive.     If  the    photosphere 
was   gaseous,   it  could  not  possibly 
maintain  the  immobility  of  its  level, 


in  the  presence  of  the  innumerable 
eruptions  which  break  through  the 
crust  in  various  places,  and  which 
would  carry  away  in  the  uprush  much 
of  the  surface  to  indefinable  distances 
from  the  avenue  of  their  escape, 
while  on  the  contrary  the  cavities 
produced  by  this  uprush  are  well  de- 
fined and  long  preserved.  The  spec- 
trum, ilso,  bears  evidence  against  the 
theory,  which  cannot  be  gainsaid. 
But  we  will  not  pursue  all  the  facts 
which  controvert  this  theory,  at  this 
point,  as  most  of  them  bear  equally 
strong  evidence  _ 
and  cloud  theories,  in 
tion  of  which  many 
will  be  reviewed. 


against  the  vapor 
the  considera- 
of  these  facts 


§  19. THE    VAPOR   THEORY. 

A  respectable  number  of  distin- 
guished physicists  conclude  the  pho- 
tosphere to  be  in  a  vaporous  condi- 
tion. Prominent  among  these  was 
Father  Secchi,  and  is  Prof.  Langley 
of  Pennsylvania.  The  former  says  : 
"  The  photosphere  is  a  mass  of  sub- 
stances, mostly  known  to  us,  raised 
to  an  enormous  temperature,  and  in 
a  state  of  vapor,  whose  spectrum  is 
rendered  continuous,  either  by  the 
heat  or  the  pressure  to  which  the 
vapor  is  subjected."  He  is,  however, 
undoubtedly  undecided  as  to  the  de- 
gree of  density  to  which  his  supposed 
"  vapor "  may  have  attained,  as  in 
the  course  of  his  elaboration,  it  will 
be  observed  that  he  conceives  it  to 
be  so  strong  in  its  connection — and 
this  is  incident  to  condensation  only 
— as  to  present  such  a  resistance  to 
the  expansive  force  within,  that  the 
latter  frequently  breaks  forth  "in 
strong  and  violent  eruptions." 

Prof.  Langley,  not  intending  to  be 
misunderstood  upon  the  question  of 
density,  says :  "  The  photosphere  is 
purely  vaporous,  and  I  consider  the 
upper  (outer)  vapors  to  be  lighter 
than  the  thinnest  cirri  of  our  own  sky." 
As  the  cirri  are  the  very  lightest  and 
least  dense  of  the  most  vague  and 
fleecy  of  the  perceptible  hazes  float- 
ing highest  in  our  sky,  we  need  not 
misapprehend  his  meaning.  Yet,  like 
Father  Secchi,  the  Professor  could  not 
have  sufficiently  studied  the  subject  to 
methodize  his  own  thoughts,  for 
later  on  he  makes  this  significant  ad- 
mission. "The  Sun  spots  give  evi- 
dence of  cyclonic  action,  such  as 
could  only  occur  in  a  fluid." 

§    20. THE    "  CLOUD-LIKE  "  THEORY. 

There  are  physicists  of  high  stand- 
ing, who,  recognizing  so  many  phy- 
sical evidences  precluding  the  con- 
clusion that  the  photosphere  can  be 
either  gaseous  or  vaporous,  say  that 
it  is  matter  in  that  condition  of  den- 
sity which  is  a  step  nearer  the  liquid 
than  vapor,  and  call  it  "  oloud-like." 


Ifl 


THE  SUN;   ITS   CONSTITUTION,  ETC. 


Of  8neh  are  Prof.  Faye  of  Paris,  and 
Prof.  YouDg  of  our  own  country. 

Prof.  Faye  in  his  incomprehensible 
manner  of  expressing  his  thoughts, 
says:  "There  are  ascending  vapors 
from  the  interior  which  go  to  form  a 
cloud  of  condensed  matter."  We 
close  the  quotation  here,  lest  if  we 
pursue  it,  the  thought  be  lost  in 
thickening  confusions. 

Prof.  Young  says:  "The  visible 
surface  of  the  Sun,  the  photosphere, 
is  composed  of  clouds  formed  by  the 
condensation  and  combination  of  such 
of  the  solar  gases  as  are  cooled  suf- 
ficiently by  their  radiation  into 
space."  Fearful  that  this  slightly 
condensed  mass  would  not  be  suf- 
ficiently strong  to  present  so  much 
hindrance  to  the  expansive  force  from 
within  as  to  produce  the  violent  erup- 
tions seen  at  the  Sun-spots,  or  entire- 
ly forgetting  the  presence  of  this  ex- 
paneive  power,  he  invents  the  follow- 
ing ingenious  theory  to  account  for 
the  explosions. 

"  The  weight  of  the  cloud-shell,  and 
the  resistance  offered  to  the  descend- 
ing products  of  condensation  (from 
the  interior  side  of  the  shell  into  the 
interior  of  the  mass),  act  to  produce 
on  the  enclosed  gaseous  core,  a  con- 
stricting pressure,  which  forces  the 
gases  upward  through  the  intervals 
between  the  clouds  with  great  veloc- 
ity." 

It  is  very  probable  that  the  Pro 
fefisor  would  be  astonished  at  the  ig- 
norance of  the  person  who,  not 
knowing  the  real  cause,  should  re- 
mark in  his  presence  that  the  heated 
gases  of  the  Earth's  interior  were 
forced  up  through  the  Earth's  crust 
at  the  volcanoes,  by  the  weight  of 
the  crust  and  the  atoms  falling  from 
its  innerside  into  the  gaseous  core ;  and 
upon  recovering  his  equilibrium, would 
correctly  inform  him  that  this  phe- 
nomenon was  produced  by  the  mighty 
expansive  power  of  the  heated  matter 
within.  Certainly  he  is  mindful  of 
the  fact  that  the  crust  of  the  Sun 
would  have  no  weight  upon  the  more 
interior  portions,  and  that  "  products 


of  condensation  r  would  not  fall  into 
the  interior  except  through  the  power 
of  attraction,  which  is  wholly  ineffect- 
ual in  the  presence  of  such  immense- 
ly high  temperature  as  reduces  mat- 
ter to  gases. 

Here  a  remark  made  by  Prof. 
Simon  Newcomb  is  apposite.  He 
says: 

"Since  the  properties  of  matter 
are  the  same  everywhere,  the  prob- 
lem of  the  physical  constitution  of  the 
Sun  is  solved  only  when  we  are  able 
to  explain  all  solar  phenomena  by 
laws  of  physics,  which  we  see  in 
operation  around  us.  The  fact  that 
the  physical  laws  operative  on  the 
Sun,  must  be,  at  least,  in  agreement 
with  those  in  operation  here,  is  not 
always  remembered  by  those  who 
have  speculated  on  the  subject.1' 

§    21. — SUPPOSED      SUPPORTS     OF     THE 
FOREGOING    THEORIES. 

The  gaseous,  vapor,  and  cloud 
theories  have  not  been  arbitrarily 
assumed,  regardless  of  facts  and  care- 
less of  consistencies,  but  on  the  con- 
trary, their  respective  advocates  seem 
driven  to  the  adoption  of  them  as  the 
only  hypotheses  upon  which  many  of 
the  solar  phenomena  can  be  at  all 
accounted  for.  Most  prominent 
among  the  phenomena,  seemingly  re- 
quiring this  rare  condition  of  matter, 
are  supposed  to  be  those  seen  in,  or 
about  the  so-called  Sun-spots.  For 
instance,  spots  have  been  observed  to 
change  their  locality  on  the  surface 
of  the  Sun,  with  a  velocity  of  1,000 
miles  in  a  second  of  time,  which,  it 
is  urged,  could  not  take  place  in  a 
density  greater  than  that  of  vapor. 
But  the  error  of  this  conclusion  lies 
in  the  thought  that  the  spots  are 
"substance  "  moving  through  matter. 
The  truth  is,  the  spets  are  only  cavi- 
ties, and  we  are  required,  not  to  con- 
ceive the  possibility  of  one  body  of 
matter  moving  through  another  at 
this  velocity,  but  only  the  possibility 
of  a  given  body  of  matter  changing 
its  own  relations  at  this  velocity  un- 
der an  inconceivably  immense  press- 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


17 


ura,  aided  by  the  most  violent  vol- 
canic action — forces  which  are  sus- 
ceptible of  gaining  such  power  as 
would  suffice  to  hurl  the  entire  body 
of  that  mighty  luminary  in  fragments 
for  millions  of  miles,  in  the  twinkling 
of  an  eye. 

A  more  prominent  phenomenon 
connected  with  these  spots  which  is 
supposed  to  require  this  rare  condi- 
tion of  matter,  is  a  supposed  sepa- 
rate arid  distinct  movement  of  them 
(the  spots)  from  the  Equator  toward 
the  poles,  and  toward  the  Equator 
from  the  latitudes,  which,  if  true,  is 
unmistakable  evidence  of  separate 
currents  of  movement  in  the  matter 
of  the  photosphere  itself — a  feature 
which  could  exist  only  in  the  rarest 
of  matter.  Upon  the  real  existence 
of  this  phenomenon  observers  are 
not  agreed.  Some  report  having 
seen  spots  move  poleward,  others  re- 
port having  seen  them  move  toward 
the  Equator,  while  others  see  nothing 
in  them  which  they  regard  as  such  a 
movement.  Prof.  Faye  denies  such 
a  motion,  and  says:  "These  strips 
(of  separate  currents,  in  which  he 
also  conceives  them  moving,  on  ac- 
count of  a  supposed  movement  other 
than  this),  move  nearly  parallel  to 
the  Equator,  and  never  give  indica- 
tions of  currents  constantly  directed 
toward  either  pole." 

Yet,  there  can  exist  no  doubt  that 
under  the  prevailing  conditions,  these 
spots  do  present  the  appearance  to 
some  minds  of  moving  longitudinally 
as  described  by  the  observers  who  re- 
port them.  That  this  is  however  an 
optical  illusion,  is  rendered  evident 
by  the  following  considerations.  Let 
a"  spot  be  selected  which  is  midway 
between  the  eastern  and  western 
limbs  of  the  Sun,  and  at  thirty  degrees 
above  the  Equator.  Here,  the  eye 
and  mind  appreciate  only  the  alti- 
tude of  the  spot  from  the  Equator, 
which,  say,  is  143,310  miles,  and  are 
wholly  unmindful  of  the  fact  that  the 
spot  is  also  farther  from  us  than  the 
Equator  by  21 ,500  miles.  The  circular 
angle  of  the  hypothenuse  of  this  tri- 


angle whose  base  is  21,500  miles,  and 
whose  altitude  is  143,310  miles  is  lost 
to  the  mind  by  the  foreshortening  in- 
cident to  its  direction  in  the  line  of 
sight.  As  the  Sun  rotates,  this  spot 
is  gradually  carried  toward  the  west- 
ern limb,  and  as  it  moves  on,  this 
angle  of  the  hypothenuse  becomes 
more  and  more  appreciable  both  to 
eye  and  mind,  until  when  the  lirnb  is 
reached,  the  angle  of  214,980  miles  is 
duly  appreciated,  and  the  spot  has 
thus  seemed  to  have  moved  a  distance 
of  71,670  miles  from  the  Equator. 
Hence,  an  observer  watching  a  spot 
passing  from  near  the  center  of  the 
Sun  toward  the  limb,  is  ready  to  as 
sert  that  it  has  in  fact  moved  from 
the  Equator.  An  opposite  illusion 
will  present  itself  to  the  person  who 
selects  a  spot  when  making  its  ap- 
pearance on  the  limb  of  the  Sun,  and 
watches  it  while  approaching  the 
center.  When  first  observed  by  him, 
his  mind  fully  appreciates  the  angle 
there  presented,  and  recognizes  the 
spot  as  being  214,980  miles  from  the 
Equator.  As  it  approaches  the  cen- 
ter, however,  this  angle  constantly 
foreshortens,  so  that  when  the  cen- 
tral position  is  reached,  the  spot 
seems  but  143,310  miles  from  the 
Equator,  and/  this  observer  is  also 
ready  to  swear  that  he  has  observed 
spots  move  toward  the  Equator.* 
Hence,  these  supposed  conflicting 
movements,  neither  of  which  is  real, 
vanish  from  the  list  of  physical  phe- 
nomena that  seem  to  render  neces- 
sary the  theories  of  extremely  rare 
matter  in  the  photosphere. 

There  is,  however,  a  supposed 
movement  of  these  spots,  which  ia 
universally  recognized  by  observers, 
and  which  serves  as  the  ruling  ne- 
cessity for  supposing  the  surface  of 
the  Sun  to  consist  of  extremely  rare 
matter.  In  the  year  1859,  Prof. 
Carrington  reported  to  the  world  of 
science,  that  the  spots  immediately 
on  or  near  the  Equator  of  the  Sun 


*  The  disk  of  the  Sun  appears  flat,  and 
neither  the  eye  nor  mind  appreciates  its  ro- 
tundity. 


18 


THE  SUN;   ITS  CONSTITUTION,  ETC. 


moved  to  the  westward  with  greater 
velocity  than  those  at  any  of  the 
latitudes,  while  the  movement  of 
spots  on  latitudes  nearest  the  Equator 
was  invariably  more  rapid  than  on 
the  latitudes  more  remote. 

Immediately  upon  this  announce- 
ment, every  telescope  in  the  civilized 
world  was  focused  upon  the  Sun- 
spots,  and  a  very  few  hours'  observa 
tLn  sufficed  to  confirm  the  dis- 
covery so  recently  made.  Whether 
•comptnion  spots  at  the  Fquator  and 
on  a  high  or  low  latitude,  or  on 
several  latitudes,  at  or  near  the  cen- 
ter, at  or  near  the  eastern  or  western 
limb  were  selected,  in  every  instance 
the  spot  on  the  Equator  was  seen  to 
move  more  rapidly  than  one  on  any 
of  the  latitudes,  while  on  any  lower 
latitude  the  motion  was  found  to  be 
more  rapid  than  on  any  higher  one — 
the  movement  regularly  decreasing 
in  velocity  on  approaching  the  poles. 
No  sooner  was  this  difference  in 
r  the  velocity  of  rotation  universally 
j  recognized  as  an  actual  physical  fact, 
than  the  savants,  knowing  the  spots 
did  not  move  tnrough  the  matter  of 
the  photosphere,  but  with  it,  wisely 
concluded  th  :t  at  least  the  outer 
<;over  of  the  photosphere,  in  which 
the  spots  moved,  was  but  a  gaseous, 
vapoious,  or  cloud  like  substance, 
moving  in  separate  currents  parallel 
to  the  Equator,  each  with  a  differing 
velocity.  M.  Fayo  formulates  the 
conclusion  as  follows: 

"  The  contiguous  strips,  (lines  of 
currents),  of  the  photosphere,  are 
animated  with  a  velocity  of  rotation 
nearly  constant  for  each  filament 
(slender  strip),  at  least  during  a  pe- 
riod of  several  months  or  years,  but 
varying  with  the  latitude  from  one 
strip  to  another." 

It  is  not  designed  to  combat  in 
detail  this  theory  of  separate  cur- 
rents or  movements,  yet  for  the  pur- 
pose of  making  apparent  the  thought- 
lessness of  many  speculators  in  con- 
structing the  premises  upon  which  to 
found  their  theory,  the  following  pro 
position  is  advanced: 


If  the  rotation  velocity  of  these 
separate  currents  on  the  photosphere 
differs  for  every  ten  degrees  of  de- 
parture f rom  the  Equator  poleward, 
then  also  must  the  velocity  of  the  cur- 
rents vary  proportionately  for  every 
ten  inches  of  distance.  'This  being 
true,  it  follows  that  however  little  the 
distance  by  which  one  spot  exceeds 
another  in  remoteness  from  the 
Equator,  there  must  be  a  difference  in 
the  velocity  of  each,  since  their  rota- 
tion velocity  is  determined  by  the 
rotation  velocity  of  tho  currents. 
Suppose  two  spots,  15,033  miles 
each  in  diameter,  tho  one  being 
1  o,003  miles  from  the  Equator, 
the  other  lying  in  right  line  at  a 
distance  of  00,000  miles  from  the 
Equator.  No\v,  suppose  a  spot  just 
westward  of  these  two  spota,  to  be 
equal  in  diameter  to  tho  diame- 
ter of  both  the  other  spots,  and 
tho  distance  dividing  them.  Each 
of  the  two  smaller  spots,  under 
the  theory,  must  be  moving  in  sepa- 
rate currents — the  difference  in  their 
velocities  being  many  hundreds  of 
miles  per  hour.  The  large  spot  must 
move  in  these  two  currents,  also,  in 
as  much  as  it  is  right  on  the  heels  of 
tho  two  others.  *"  Now,  will  these 
theorists  inform  us  why  it  is  that 
the  large  spot  is  not  torn  into  frag- 
ments by  these  separate  currents  of 
different  velocities?  Large  spots 
and  smaller  ones  aro  seen  moving 
without  disturbance,  in  clusters, 
every  year,  right  in  the  face  of  these 
theorists,  who  appear  never  to  have 
noticed  them,  or  if  so,  regarding  the 
phenomena  as  of  vastly  less  import- 
ance than  their  theories. 

The  truth  concerning  this  rotary 
velocity  of  the  spots  is  quickly  told. 
There  is  precisely  that  difference  in 
the  speed  with  which  they  rotate  at, 
or  away  from  the  Equator, which  Prof. 
Carrington  has  reported.  He  made 
separate  daily  observations  of  spots 
upon  the  Equator,  and  found  the 
daily  angular  velocity  of  rotation  to 
be  865',  while  several  daily  observa- 
tions of  spots  at  latitude  30°,  showed: 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


19 


their  daily  angular  velocity  to  be 
816'.  From  these  observations  it 
was  deduced  as  a  legitimate  mathe- 
matical conclusion,  that  as  the  latitu- 
dinal spot  moved  slower  by  49'  daily 
than  a  spot  on  the  Equator,  it  would 
require  one  more  day  to  complete 
its  revolution — and  hence  the  move- 
ments are,  and  must  be  separate. 
The  error  of  this  conclusion  is  ren- 
dered apparent  by  the  statement  of 
a  few  very  simple  mathematical  pro- 
positions. 

The  Sun  at  the  Equator  is  860,000 
miles  in  diameter,  and  in  round  num- 
bers 2,580,000  miles  in  circumfer- 
ence. At  a  latitude  of  30°,  suppos- 
ing it  to  be  a  perfect  sphere,  it  is 
81 7,000  miles  in  diameter,  and  2,450,- 
000  miles  in  circumference.  It  is 
evident  that  a  spot  on  the  Equator 
would  be  required  to  travel  103,200 
miles  daily,  in  order  to  complete  its 
circuit  in  twenty-five  days,  while  a 
spot  at  30°  latitude  could  make  its 
circuit  in  twenty-five  days  if  it  trav- 
eled but  98,000  miles  per  day.  In 
other  words,  the  latitudinal  spot 
traveling  5,160  miles  less  each  day 
would  complete  a  rotation  of  its 
smaller  circuit  in  the  same  period  of 
time  occupied  by  the  equatorial  spot 
in  making  its  correspondingly  greater 
one.  Hence  the  matter  of  the  pho 
tosphere  at  the  Equator,  and  at  the 
latitude  of  30°,  has  not  changed  its 
relative  position  notwithstanding  this 
difference  in  rotary  velocity.  The 
same  results  would  be  present  on  a 
globe  of  the  most  solid  iron. 

Here  observers  have  not  been  mis- 
led by  an  optical  illusion,  but  have 
erred  by  drawing  a  conclusion  from 
a  partial  fact  only.  Prof  Carrington 
and  other  observers  have  noted  the 
rate  of  speed  with  which  a  spot  on 
the  Equator  moved  for  a  few  days, 
then  in  like  manner  the  rate  with 
which  a  spot  on  some  of  the  latitudes 
has  moved ;  and  discovering  the  dif- 
ferences in  the  rate  of  velocity — 
without  stopping  to  consider  the  dif- 
ference in  the  distances  which  each 
had  \o  move  on  account  of  the  rotun- 


dity of  the  body — have  drawn  the 
erroneous  conclusion  referred  to,  and 
which  has  forced  many  a  deluded 
spectator,  like  M.  Faye,  to  rack  his 
brain  over  every  species  of  currents, 
except  a  current  of  thought  toward 
the  misleading  error  of  deduction. 
It  must  now,  however,  be  deemed 
conclusively  settled  that  the  differ- 
ence in  the  velocity  of  the  spots  at 
the  Equator  and  latitudes  is  no  evi- 
dence of  a  movement  of  the  matter 
constituting  the  photosphere,  and 
hence  presents  no  necessity  for  the 
assumption  of  matter  in  so  rare  a 
condition  as  gas,  vapor  or  cloud. 

There  are,  however,  many  physical 
facts  now  known  of  the  Sun  which 
bear  strong  evidence  against  so  rare 
a  condition  of  matter  at  its  surface. 
The  spectrum  assures  us  of  an  inten- 
sity in  its  heat  which  could  not  possi- 
bly be  attained  and  held  by  matter 
so  rare.  This  spectrum  is  neither  of 
lineal  nor  of  fluted  bands,  as  would 
be  the  case  if  the  molecules  were  in 
so  imperfect  contact  as  indicates 
gaseous  or  vaporous  conditions,  but 
on  the  contrary  its  continuous  fea- 
ture is  conclusive  evidence  of  matter 
in  a  state  not  less  dense,  at  least,  than 
fluid.  The  difference  in  the  rotating 
velocities  of  the  spots,  which  was  so 
long  regarded  as  conclusive  evidence 
of  matter  in  a  very  rare  state,  must 
now  be  held  to  be  as  conclusive  proof 
that  this  surface  is  in  a  condition 
which  at  all  points  maintains  its  re- 
lations ;  and  to  this  extent  is  evidence 
against  either  a  gaseous,  vaporous  or 
cloud-like  density.  The  absence  of 
oblateness  in  the  Sun,  with  its  velo- 
city of  rotation,  is  also  conclusive 
evidence  against  these  theories,  it 
being  incontestable  that  centrifugal 
force  arising  from  a  given  rotary 
velocity  will  posses  an  effective  power 
proportionate  to  the  rarity  of  the 
matter  on  which  it  operates.  The 
photosphere  could  not,  in  the  presence 
of  such  frequent  and  violent  eruptions 
as  admittedly  prevail  there,  main- 
tain its  continuous  level  and  un- 
changing rotundity  if  in  so  rare  a 


20  THE  SUN ;  ITS  CONSTITUTION,  ETC. 

condition,  but  on  the  contrary,  large  be  required  to  contract  but  220  feet 
portions  of  it  would  be  continuously :  a  year  in  order  to  produce  its  present 
displaced.  Again,  such  violent  erup  |  heat.*  We  are  not  aware  of  the  basis 
tions  could  not  possibly  obtain  in  a '  of  this  calculation,  but  it  is  evident 
body  whose  surface  afforded  no  great  that  the  contraction  would  have  to 
er  resistance  to  the  expansive  force  exceed  these  figures  very  largely,  if 
of  the  interior  heat  than  would  be  |  the  matter  be  more  rare  than  quite  a 
presented  by  gases,  vapors  or  clouds.  |  dense  fluid. 

Still  again,  in  such  light  and  easily  j  At  this  point,  however,  it  may  be 
disturbed  matter  the  spots  would  not  I  well  to  suggest  that  attraction  exerts 
and  could  not  maintain  their  existence,  I  no  pressure  upon  gases — atoms  in  a 
their  forms,  and  even  the  minutiae  of  j  state  of  commotion  called  heat — al- 
their  projections,  depressions  and  !  though  it  will  exert  a  drawing  pressure 


sharp  angles  for  mouths,  as  they  are 
known  to  do. 

Another  disproving  physical  fact 
is  found  in  the  method  by  which  the 
heat  supply  is  maintained  in  the  Sun. 
However  wild  or  unnatural  may  be 
the  theories  of  most  speculators  con- 
cerning the  Sun  in  relation  to  all  else, 
they  are  each,  by  our  advanced  knowl- 
edge of  this  subject,  compelled  to  ad- 
mit that  the  heat  of  the  Sun  is  en- 
gendered by  the  friction  between 
atoms  when  coming  in  contact,  while 
in  process  of  contraction  or  conden- 
sation, to  produce  which,  the  outer 
.atoms  move  inward  If  it  were  ne- 
cessary that  the  atoms  should  move 
to  any  considerable  distance  to  be 
brought  in  contact,  the  Sun  would 
diminish  in  dimensions  rapidly.  In 
matter  as  rare  as  gas,  vapor  or  clouds, 
the  atoms  are  so  remote  from  each 
other,  that  in  order  to  bring  them 
into  actual  contact,  a  considerable 
movement  would  be  required.*  We 
have  no  evidence  of  any  perceptible 
diminution  in  the  size  of  the  Sun 
since  man  first  measured  its  disk ; 
while  the  angle  which  it  distends 
would  have  grown  visibly  less  in  that 


gaseous   and 
must     either 


upon  atoms  in  a  state  of  quietude,  when 
they  are  no  longer  gases,  but  atomic 
substances  —  and  that  if  the  surface  of 
the  Sun  is  gaseous,  there  is  no  power 
to  hold  them  in  contact,  nor  cause 
them  to  draw  closer  together.  Hence 
the  advocates  of  the 
vaporous  conditions 
abandon  their  theories,  or  disprove 
that  the  heat  supply  of  tho  Sun  is 
kept  up  by  the  process  of  contrac- 
tion. 

§    22.  -  TIIK    CRUST    IN     A      FLUID     CON- 
DITION. 

A  few  words  now  concerning  the 
theory  that  the  Sun  crust  is  a  fluid. 
But  few  modern  scientists  have  had 
the  hardihood  to  urge  this  theory  in 
the  face  of  the  many  apparent  facts 
BO  long  and  so  forcibly  presented  as 
proofs  of  matter  in  a  rarer  condition 


pecially  those  supposed  to  exist 
in  the  movements  of  the  Sun  spots. 
Yet  some  of  the  very  ablest  of  rea- 
soners,  without  attempting  to  account 
for  these  movements,  but  intuitively 
feeling  that  they  had  not  yet  been 
clearly  nor  correctly  understood,  af- 
ter viewing  the  whole  field  and  seeing 


period,  were  the  matter  of  which  its  |  so  many  piain  ana  incontestable  phe- 
surface  is  composed  so  rare.     Philo- 
sophically, we  are  constrained  to  ad 


mit  that  in  order  to  maintain  the 
heat  supply,  that  body  is  in  fact  con- 
tracting in  size,  yet  it  must  be  slowly. 
An  estimate  has  been  made  in  which 
it  was  concluded  that  the  Sun  would 


*  It  is  unphilosophical  to  think  of  the  phe- 
nomenon of  heat  being  produced  without  a 
contact  of  the  atoms. 


nomena  in  absolute  conflict  with  the 
conclusions  of  the  theorists,  have  de- 
clined to  accept  either  the  gas,  vapor 
or  cloud  hypothesis.  Most  prominent 
of  this  class  of  independent  thinkers 
stands  Prof.  Simon  Ne \vcomb,  who, 
while  dissenting  from  these  theories 
and  declining  to  present  one  in  their 


Newcomb's  Astronomy,  page  519... 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


stead,  yet  suggests  one  in  very  sig- 
nificant language  when  he  says: 

"The  opinions  of  students  respect- 
ing the  constitution  of  the  photo- 
sphere, are  so  different  that  it  is  hard 
ly  possible  to  express  any  views  that 
will  not  be  challenged  in  some 
quarter.  Although  a  contrary  opin- 
ion is  held  by  many,  we  may  venture 
to  say  that  the  rays  of  light  and  heat 
aeem  to  come  not  from  a^as,  but  from 


solid  matter.  This  is  indicated  by 
the  fact  that  their  spectrum  is  con- 
tinuous, and  also  by  the  intensity  of 
the  light  which  far  exceeds  any  that 
as  has  been  made  to  give  forth 
t  does  not  follow  from  this  that  the 
photosphere  is  a  continuous  solid  or 
crust,  since  floating  particles  of  solid 
matter  will  shine  in  the  same  way. 
That  it  is  not  continuously  solid,  like 
our  earth,  seems  to  be  fully  shown  by 
the  variations  and  motions  of  the 
spots,  which  have  every  appearance 
of  going  on  in  a  fluid."* 

All  the  reasons  which  have  been 
advanced  against  the  gas,  vapor,  and 
cloud  theories,  are  equally  effective 
affirmative  supports  of  the  hypothesis 
that  the  photospheric  matter  is  in  a 
condition  at  least  as  dense  as  the 
very  densest  of  all  our  fluids.  In 
the  face  of  the  frequent  changes 
which  are  seen  in  the  Sun-spots,  no 
one  would  have  the  temerity  to  re- 
gard the  matter  as  solid. 

That  this  fluid  must  have  a  density 
beyond  that  of  water,  is  made  evi- 
dent by  the  persistency  with  which 
the  very  details  of  the  spots  are 


sity  of  mater  must  be  found  in  this 
crust.  It  has  been  for  years  conced- 
ed by  physicists,  that  taking  the  vol- 
ume of  space  occupied  by,  and  the 
force  of  gravity  in  the  Sun  into  con- 
sideration it  was  a  correct  deduction, 
upon  a  strictly  mathematical  basis, 
to  say  that  tho  density  of  the  body, 
as  a  whole,  was  greater  than  water 
by  1.414.  This  being  true,  and  who 
would  now  dispute  it?  and  it  be- 
ing further  true  that  by  far  the  great- 
er density  of  the  body  must  exist  in 
this  crust,  it  follows  as  an  irresisti- 
ble and  incontrovertable  conclusion, 
that  the  matter  of  the  Sim's  photo- 
sphere is  in  a  condition  far  denser 
than  water. 

Considering  how  vastly  inferior  in 
quantity  of  matter  this  crust  must  be 
when  compared  with  the  immense 
interior,  it  would  not  be  entirely  em- 
pirical to  say,  that  the  matter  of  this 
crust  is  as  dense  as  tar,  or  not  greatly 
unlike  heated  iron  in  that  condition 
when  it  is  fitted  to  run  into  molds. 

§  23. PRODUCTION  OF  THE  SUN  SPOTS. 

With  matter  of  such  density  form 
ing  the  crust  of  the  Sun,  there  can  be 
no  difficulty  in  understanding  how  it 
presents  a  resistive  force  to  the  ex- 
pansive power  of  the  heated  matter 
within,  nor  will  doubts  exist  in  the 
mind  of  the  observer  as  to  the  suffi- 
ciency of  this  resistance,  when  over- 
come by  a  superior  power,  to  pro- 
duce such  violent  eruptions  as  not 
only  form  immense  cavities  within 
its  depths,  but  whose  lateral  pressures 


maintained,  as  well  as  by  the  well  de- j  serve  as  successful  aids  in  their  long 

maintenance.    So  can  it  be  easily  un- 
derstood how  the  violent  uprushof  the 


fined  forms  into  which  it  is  broken 
by  the  violent  eruptions  on  the  break- 
ing out  of  these  spots.  A  more  con- 
clusive fact  on  this  point  is  found  in 
the  following  relations.  It  is  con- 
ceded that  the  entire  central  region 
of  the  Sun,  indeed  all  but  a  mere 
exterior  crust,  is  in  a  highly  gaseous 
state,  whose  density  must  be  rare, 
very  rare,  and  that  the  greater  den- 


*  We  omit  the  words  *porgas"  here  for 
the  reason  that  he  immediately  proceeds  to 
show  it  could  not  be  gas. 


erupted  matter,  following,  of  course, 
the  radii  of  the  sphere,  produces 
cavities  not  unlike  inverted  cones  in 
form,  the  angles  of  whose  *udes  are 
made  greater  than  the  angle  of  the 
radii  by  the  wash  incident  to  the 
lateral  pressure  of  the  out-rushing 
metallic  gases,  thus  producing  the 
penumbra  of  these  spots,  the  lines  of 
projections  and  depressions  precisely 
as  they  are  seen  by  the  telescope. 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


§    24. THE    AREA    OF    SUN    SPOTS     LIM-  | 

ITED. 

We  are  aware  that  the  outward 
pressure  of  these  interim  expanding 
gases  would  be  equal  on  every  con- 
ceivable portion  of  the  enclosing 
spherical  walls  presented  by  this 
crust,  and  that,  under  this  sole  influ- 
ence evidences  of  these  eruptions 
would  be  as  likely  to  be  seen  on  one 
portion  of  the  surface  of  the  Sun,  as 
on  another;  while  in  truth  but  one 
instance  has  been  known  of  an  erup- 
tion above  40°  latitude,  though  thou- 
sands have  been  observed  on  and  near 
the  Equator,  From  a  series  of  ob- 
servations extending  over  a  period  of 
ten  years,  and  comprehending  1,700 
spots,  Prof.  Loomis  compiles  the  fol- 
lowing table,  giving  the  per  centage 
of  their  occurrence  m  different  locali- 
ties: 


LOCATION    OF  SPOTS. 

j 

q 
s 

•7 

•3 

ii 

LOCATION   OF   SPOTS. 

m 

M 

Beyond  30°  North  L  at. 
Between  20  &  30° 

"           10  &  20°      " 

M         o&io°    »» 

Beyond  30°  South  Lat 
Between  ao  &  39°    " 

"           10  &  20*      " 

"         o&io"    " 

2 
15 

»7 

12 

By  this  table  it  is  seen  that  twenty- 
three  per  cent,  of  the  spots  appear 
upon  or  within  ten  degrees  of  the 
Equator,  and  sixty-three  per  cent, 
within  twenty  degrees,  while  but 
thirty-seven  per  cent,  occur  at  a 
greater  distance,  and  comparatively 
none  beyond  thirty  degrees.  No  one 
has  ever  attempted  to  account  for  this 
limitation  of  the  Sun  spot  area. 
Faye,  Langley,  Young  and  New- 
comb,  are  silent  upon  this  subject, 
while  Father  Secchi  says,  "  It  is  re- 
markable that  the  parallel  of  thirty 
degrees  divides  the  hemisphere  into 
two  sections  of  equal  volume."  He 
further  recognizes  these  sections  as 
exceeding  all  others  in  activity,  but 
does  not  attempt  to  show  why  it  is 
so.  Yet,  in  concluding  that  these  are 
the  most  active  regions  of  the  Sun, 
the  learned  observer  has  mistaken 
evidence  of  activity  for  activity  itself. 
The  spots  are  but  evidence  of  inte 


rior  activity,  which  has  made  itself 
apparent  in  these  particular  regions 
only,  owing  to  some  cause  which  he 
has  not  sought  to  divine,  but  which 
is  explicable  on  the  most  satisfactory 
basis. 

The  expansive  force  of  the  strug- 
gling interior  heat  is  exerted  equally 
upon  all  sides  of  the  enclosing  walls 
— the  crust — and  would  break  through 
wherever  these  walls  were  weakest; 
and  if  they  were  constructed  by  a 
uniform  force — attraction  or  gravita- 
tion— there  can  be  no  reasons  for 
supposing  them  to  be  weakest  in  the 
region  of  the  Equator.  What  would 
be  equal  to  such  a  weak  spot  in  the 
walls,  however,  would  be  some  force 
acting  in  conjunction  with  the  expan- 
sive force  at  some  points  on  the 
crust  which  did  not  combine  with  it 
in  equal  power  at  other  points.  Is 
there  such  a  combination  of  forces  at 
or  near  the  Equator? 

The  Sun  is  rotating  on  an  axis  once 
in  every  twenty-five  days.  The  cir- 
cumference at  its  Equator  is  about 
2,580,000  miles,  and  hence  a  given 
point  upon  it  moves  through  space  at 
the  rate  of  103,200  miles  per  day, 
4,300  miles  per  hour,  and  one  mile 
and  eighteen-one  hundredths  of  a 
mile  for  every  second  of  time.  It  is 
known  that  rotary  motion  engenders 
centrifugal  force  and  that  the  degree 
of  this  force  is  proportionate  to  the 
velocity.  With  a  velocity  as  great  as 
that  prevailing  at  the  Equator  of  the 
Sun,  this  power,  which  would  draw 
the  matter  away  from  the  center  and 
hurl  it  into  space,  must  be  immense. 
This  force,  however,  while  greatest 
at  the  Equator,  is  existent  at  every 
conceivable  degree  of  latitude,  lessen- 
ing regularly  in  power,  of  course, 
with  the  decrease  of  velocity,  as  ob- 
served on  approaching  the  poles,  un- 
til when  forty  degrees  are  reached, 
the  power  is  very  weak,  as  the  ve- 
locity is  very  slow. 

While  the  centrifugal  force  would 
be  greatest  on,  and  in  the  immediate 
vicinity  of  the  Equator,  yet  it  would 
not  materially  vary  in  power  for  the 


THE  SUN;  ITS   CONSTITUTION,  ETC. 


first  few  degrees  removed,  and  a 
slight  inherent  weakness  in  the  crust 
at  these  points  would  equal  the  dif- 
ference in  the  strength  of  the  centri 
f ugal  force.  It  is  not  entirely  specu 
lative  to  conclude  that  this  identica" 
centrifugal  force,  during  the  process 
of  condensation  has  weakened  the 
crust  at  some  little  distance  from  the 
Equator  on  either  hand,  by  draw- 
ing down  to  the  Equator  from  these 
regions,  matter  which  the  attrative 
force  would  otherwise  have  distribu- 
ted equally  throughout  the  condensed 
crust.  Hence  it  is  seen  that  the  two 
forces,  centrifugal  and  expansive, 
have  combined  most  effectively  in  the 
very  region  of  the  photosphere  where 
these  spots  are  found  to  be  most  fre- 
quent and  most  active. 

Who  will  doubt  that  these  forces 
determine  the  region  of  the  Sun 
spots. 

§    25. PERIODICITY    OF    THE    SPOTS. 

It  is  also  urged  that  the  expansive 
and  centrifugal  forces  are  constan  t,  and 
that  under  like  prevailing  conditions 
they  must  produce  continuous  and 
uniform  results,  while  the  frequency 
and  activity  of  the  spots  vary  in  pe- 
riods of  time.  But  it  must  not  be 
forgotten  that  their  variance  has 
about  it,  in  a  general  way,  such  reg- 
ularity as  to  approach  periodicity. 

There  is  a  period  when  in  fre- 
quency, numbers  and  activity  they 
are  at  their  higtit;  then  they  begin 
to  decline  in  these  particulars,  and 
continue  so  to  do  for  five  or  six  years, 
at  which  period  they  reach  the  mini- 
mum of  activity ;  again  their  fre- 
quency, number  and  activity  begin  to 
increase,  and  continue  so  to  do  for 
five  or  six  years,  when  they  reach 
again  the  maximum — the  period 
from  one  highest  point  to  another,  or 
from  one  lowest  point  to  another, 
generally  being  found  to  be  about 
eleven  years. 

Prof.  Newcomb  says  of  this  pe- 
riodicity, that  no  satisfactory  explana- 
tion of  its  cause  has  yet  been  given. 
Father  Secchi  says :  "  Whatever 


may  be  the  cause  of  thesa  changes 
of  activity,  we  are  completely  ignor- 
ant of  it.  M.  Faye,  who  does  not 
seem  inclined  to  acknowledge  a  want 
of  full  knowledge  on  any  topic  touch- 
ing the  Sun,  yet  says  of  this:  "It  is 
mure  difficult  to  account  for  the  pe~ 
riodicity  of  the  spots."  Prof.  Young- 
says  :  "  I  am  unable  to  think  the  pe- 
riodicity of  the  spots  due  in  any- 
way to  planetary  action  ;*  at  leasty 
the  evidence  appears  to  me  wholly  in- 
sufficient as  yet,  but  I  have  no  hy- 
pothesis to  offer." 

Upon  the  hypothesis  of  the  expan- 
sive power  of  the  interior  gases,  this 
phenomenon  is  susceptible  of  the  mo^t 
satisfactory  explanation.  All  are 
aware  that  the  longer  we  successfully 
restrain  engendering  steam,  thegreat- 
er  the  power  it  attains.  We  are  also- 
aware  that  when  the  pressure  of  the 
steam  has  reached  a  high  point,  if  we 
permit  some  portion  of  it  to  escape, 
the  pressure  is  relieved  just  to  the  ex- 
tent of  the  escape.  Upon  closing 
the  avenue  of  escape,  the  steam  again 
begins  to  gain  head  and  pressure,  and 
will  repeat  this  ebb  and  flow  just  so 
many  times  as  we  open  and  close  the 
escape.  Suppose,  now,  in  the  case  of 
the  Sun  that  a  large  number  of  spots 
appear,  through  which  the  heated 
gases  from  within  are  permitted  to- 
escape  in  immense  volume  for  days. 
While  this  escape  is  going  on,  the 
pressure  is  being  relieved  precisely  in 
proportion  to  the  amount  of  matter 
which  has  been  ejected,  and  as  this 
pressure  decreases,  there  is  a  corres- 
ponding decrease  in  the  number  of 
lew  cavities  produced.  Finally,  the 
entire  pressure  outward  is  exhausted, 
when  the  lateral  pressure  of  the  es- 
caping gases  is  withdrawn  from  the 
sides  of  the  eavities,  which  are  then 
'orced  inward  by  the  pressure  of  the 
iquid  matter  of  the  crust,  in  an  effort 
o  seek  a  level,  and  the  cavities  are 
;losed.  Upon  the  closing  of  these 


*  Strange  to  say,  many  learned  men  have 
attributed  this  periodicity  to  Jupiter,  whose 
eriod  of  revolution  is  somewhat  coincident 
with  them. 


24 


THE  SUN.;   ITS  CONSTITUTION,  ETC. 


cavities,  or  avenues  of  escape,  the  in- 
terior heat  begins  to  gain  head  and 
continues  to  do  so  until  it  (in  combi 
nation  with  the  centrifugal  force)  be- 
comes superior  to  the  force  of  resist 
ance  arrayed  against  it  by  the  crust, 
when  it  again  breaks  forth  in  all  its 
first  vigor.  Thus,  the  expansive  force 
furnishes  the  causes  for  its  periods  of 
activity  and  exhaustion.  Could  any 
thing  be  more  evident? 

But,  it  may  here  be  asked,  why  are 
these  vibrations  from  one  extreme  to 
the  other  measured  by  comparatively 
equal  periods  of  time.  The  answer 
is  found  in  this  proposition :  The 
same  constant  forces  acting  upon  the 
same  volume  of  matter  under  like  re- 
curring conditions  must  prodi.se  uni- 
form results.  It  is  evident  that  so 
fast  as  the  matter  of  the  interior  of 
the  Sun  is  thrown  by  the  eruptions 
into  the  sin-rounding  atmosphere,  it  is 
cooled,  and  by  the  force  of  attraction 
brought  back  to  the  outer  surface  of 
the  crust,  where  it  enters  into  the  pro- 
cess of  condensation,  supplying  to  the 
exterior  the  identical  matter  taken 
from  the  interior  while  the  interior 
itself  is  refilled  by  the  contraction  of 
the  more  outward  portions.  Thus, 
for  ages,  will  the  same  forces  exist 
and  continue  their  work  upon  the 
same  volume  of  matter  restored  by- 
repeated  processes  under  like  condi- 
tions, and,  if  one  century  ago  it  re- 
quired eleven  years  to  complete  the 
circuit  of  this  work,  there  remains  no 
reason  why  it  should  not  require  about 
eleven  years  to  repeat  it  again  one 
hundred  years  hence.  True,  the  causes 
would  not  produce  a  companion  re- 
sult again  in  precisely  the  same  pe- 
riod as  before — often  not  within  a 
year,  perhaps  not  within  two,  and  at 
times  not  within  three  years;  nor  are 
the  maxima  of  these  spots  more  reg- 
ular than  this,  as  will  bo  seen  by  ob- 
serving the  table  prepared  by  any  ob- 
server. 

$    26  THE      SPOTS     AHK     CAVITIES     IN 

THE    SUN. 

Although  much  space  has  been  oc- 


cupied in  considering  this  particular 
phenomenon,  yet  it  would  be  improp- 
er to  omit  a  notice  of  the  proof  ad- 
duced by  observation  of  the  concavity 
of  these  spots. 

As  early  as  1684,  Cassini,  one  of 
the  first  observers  with  the  telescope, 
declared  that  he  had  seen  a  notch  in 
the  limb  of  the  Sun,  directly  upon  the 
point  where  a  Sun-spot  was  just  go- 
ing off.  Since  his  time,  a  number  of 
other  observers  have  witnessed  the 
same  appearance,  both  when  the 
snots  were  coming  on  and  going  off. 
If  further  proof  of  this  concavity 
were  needed,  it  is  abundantly  afforded 
in  the  perspective  presented  by  them 
while  passing  from  one  limb  to  the 
other.  In  1869  Prof.  Wilson,  of 
Glasgow,  made  such  close  examina- 
tion of  a  series  of  spots,  for  the  pin 
pose  of  ascertaining  the  real  facts  of 
this  phenomenon,  that  no  physicist 
now  doubts  that  these  spots  are  im- 
mense cavities  in  the  crust  of  the  Sun. 
From  the  angles  presented  by  the 
changes  made  in  the  penumbra,  Wil- 
son estimated  the  depth  of  the  crust 
to  be  4,000  miles,  which  is  in  effect, 
an  estimate  that  for  a  distance  of  4,- 
000  miles,  the  crust  is  sufficiently 
dense  to  preserve  form  and  maintain 
distinctive  features. 

Other  estimates  have  been  made 
upon  like  observations  with  some- 
what varying  results,  Prof.  Young 
concluding  that  the  crust  could  not 
|  be  less  than  10,000  miles  in  thickness. 
These  spots,  then,  are  found  to  be 
immense  hole.*?  in  the  body  of  the  Sun. 
whose  diameters  range  from  13,000 
to  100,000  miles,  and  whose  depth  is 
estimated  from  4,000  to  10,000  miles. 

The  walls  or  sides  of  the  cavities 
form  what  is  called  the  penumbru. 
and  to  an  imperfect  or  weak  instru- 
ment present  the  appearance  of  u 
broad  inner  rim,  extending  from  the 
outer  circumference  cenlerward,  to  a 
more  central  portion  of  the  spot, 
which  is  darker  in  color,  and  called 
the  nucleus.  These  walls  are  not  of 
uniform  color,  but  are  streaked  with 
light  and  darker  lines,  running  from 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


25 


the  exterior  to  the  interior,  and  pre- 
senting to  the  eye  the  appearance  of 
washes  or  gutters  on  a  clay -bank  or 
hill-side.  While  the  central  portion 
of  the  nucleus  is  darker  in  color  than 
the  penumbra,  it  is  by  no  means  black, 
nor  does  it  appear  to  serve  as  the 
bottom  of  the  cavity.  Rather  it  pre- 
sents the  appearance  of  being  the  dim 
light  of  luminous  vapor  away  down  in 
the  regions  of  the  solar  interior  seen 
through  these  openings  in  the  crust. 

By  a  close  observation  it  will  be 
ascertained  that  the  eruptions  from 
the  spots  are  most  active  upon  their 
first  appearance,  during  which  time 
the  spectroscope  detects  among  the 
escaping  gases  those  of  the  heaviest 
metals,  such  as  iron,  nickel,  magne- 
sium, and  sodium,  while  as  the  activ- 
ity subsides  their  presence  grows  less 
frequent,  until  when  the  spot  is  on 
the  point  of  closing  up  they  are  not 
seen  at  all.  When  the  spots  are 
most  active  the  faculse  heretofore 
spoken  of  are  most  generally  seen. 
It  has  been  shown  that  these  fac- 
ulae  are  but  the  prominences  seen 
during  an  eclipse,  and  recognized  as 
glowing  hydrogen  flames  shooting  out 
with  inconceivable  velocity  through 
the  chromosphere,  and  in  the  direc- 
tion of  the  Corona. 

When  we  consider  the  mighty 
fires  which  are  raging  within  the 
interior  of  this  vast  body,  the  Sun, 
and  the  irresistible  power  of  the 
expansive  force  created  by  it,  in 
connection  with  the  immense  resist 
ive  force  which  must  be  presented  by 
a  crust  of  such  density  and  depth,  it 
will  not  be  deemed  marvelous  that  at 
times  the  heated  gases  break  forth 
with  an  explosive  power  so  great  as 
to  hurl  them  into  space  through 
these  cavities  in  the  direction  of  the 
faculae  and  prominences,  until  the 
lightest  of  them  is  seen  in  the  Co- 
rona and  even  in  the  projections,  a 
distance  of  not  less  than  three  hun- 
dred thousand  miles.* 


*  Some  have  estimated  this  power  to  be 
sufficient  to  hurl  the  matter  to  a  distance 
equal  to  that  of  the  Asteroids  from  the  Sun. 


§  27. HOW  THE  HEAT  OF  THB  SUN 

REACHES  THE  EARTH. 

Having  ascertained  the  manner  in 
which  the  heat  of  the  Sun  is  engen- 
dered, it  becomes  of  interest  to  know 
how  that  heat  is  communicated  to 
the  Earth  and  other  planets  of  the 
solar  system.  We  have  learned 
that  the  phenomenon  which  we  call 
the  heat  of  the  Sun  is  but  an  active 
commotion  among  its  coastituent 
particles,  as  all  heat  is  but  motion  in 
atoms  of  matter. 

We  have  now  but  to  ascertain 
in  what  manner  the  commotion  in 
the  atoms  of  the  Sun  can  be  commu- 
nicated to  the  atoms  comprising  the 
Earth  or  the  other  planets  of  this 
system. 

In  the  first  place,  it  is  no  longer 
held  among  scientists  that  the  at- 
mospheres of  the  Sun  and  its  satellites 
are  each  limited  in  extent,  and  bound- 
ed by  clearly  defined  lines,  the  spaces 
between  being  void  of  matter,  and 
hence  vacuums ;  but,  on  the  cor- 
trary,  it  is  no*v  admitted  by  nearly 
all  physicists  that  the  respective  at- 
mospheres of  all  the  planets,  and  of 
the  Sun,  are  densest  at  the  surface 
of  the  bodies,  gradually  growing 
more  rare  outward  until  at  length 
but  one  substance  constitutes  it,  and 
that  substance  a  very  rare  one  in- 
deed. For  the  want  of  a  more  spe- 
cific name  the  terms  "  luminiferous 
ether  "  and  "interstellar  ether"  are 
used  to  distinguish  it  from  the 
other  substance  in  Nature.  This 
ether  pervades  all  space  everywhere 
and  in  all  directions.  It  not  only 
fills  the  space  lying  between  neigh- 
boring planets,  "but  also  all  space, 
however  small,  existing  between  each 
atom  of  matter  constituting  the  plan- 
ets and  their  atmospheres.  Hence, 
all  the  way  along  the  92,700.000 
miles  from  the  Sun  to  the  Earth  this 
ether  exists,  starting  from  within  the 
surface  of  that  luminary  in  the  di- 
rection of  every  conceivable  radius  of 
that  spherical  body,  filling  the  inter- 
stices between  the  atoms  composing 


THE  SUN;   ITS   CONSTITUTION,  ETC. 


the  chromosphere,  as  well  as  those  of  j  municated  to  the  atoms  composing 
its  cooler  atmosphere,  and  when  '  our  atmosphere,  as  well  as  to  all  other 
reaching  a  point  still  further  outward  |  matter  on  or  about  the  surface  of  the 
where  no  other  substance  is  encoun-j  Earth.  This  motion  of  the  atoms  so 
tered,  it  occupies  the  entire  dominion. ;  differs  in  certain  particulars  from  nil 


Reaching  the  outermost  regions  of 
the  atmosphere  of  the  Earth,  or 
any  other  of  the  planets,  it  mingles 
with  the  atmospheric  gases,  filling 
up  the  interstices,  and  pressing  on- 
ward to  the  surface  of  the  planet 
wher^  it  in  like  manner  crowds  itself 
into  every  space,  whether  it  be  cavity 
or  pore,  of  the  body  itself. 


other  motion  in  matter,  as  to  produce 
upon  the  sentient  nerves  by  contact 
a  sensation  so  different  from  all  other 
sensations  as  to  be  readily  identified; 
and  this  sensation  we  have  denomi- 
nated heat. 

It  is  not  within  the  legitimate  prov- 
ince of  this  essay  to  describe  the 
phenomenon  of  heat  and  its  method 


While  this  ether,  from  its  nature, '  of  transmission,    yet  it   will  not  be 


is  wholly  im perturbed  by  attraction 
or  gravitation,  yet  it  is  extremely 
sensitive  to  every  other  known  force. 
Like  all  other  matter  it  is  unquestion- 
ably composed  of  atoms,  but  whether 
its  combination  is  complete  in  the 
single  atom,  as  in  mercury,  or  whether 
two  or  more  of  these  atoms  are  com 
bined  into  molecules,  is  unknown, 
but  the  chromic  effects  of  light  can  be 
best  accounted  for  upon  the  hypothe- 
sis that  it  is  molecular  and  that  its 
molecules  are  composed  of  not  less 
than  two,  nor  more  than  three  atoms. 
Although  thus  combining  with  itself, 
it  has  no  affinity  for  other  substances, 
and  hence  is  never  disturbed  by  ab- 
sorption or  combinations,  and  there- 
fore ever  presents  the  same  volume 
and  maintains  the  same  universal 
profusion. 


wholly  out  of  place  to  say  that  the 
motion  of  the  atoms  is  transmitted 
through  space  by  this  medium,  in  a 
tremulous  or  vibratory  movement  that 
goes  onward  at  a  rate  of  speed  which 
is  ever  indicative  of  the  degree  of 
activity  in  the  commotion  among  the 
particles  or  atoms  of  the  heated  body 
radiating  them.  Hence,  if  the  com- 
motion in  the  Sun  is  very  intense— 
that  is,  if  the  heat  be  high — the  undu- 
lations will  be  very  rapid,  while  if  the 
commotion  be  less  active,  the  undula 
tionj  will  be  slower. 

Thus,  the  rate  of  speed  observed  in 
the  so  called  heat-waves  is  evidence 
of  the  degree  of  heat  attained  in  the 
emitting  body. 

As  the  heat  in  the  Sun  is  intense, 
the  vibrations  of  its  heat-waves  are 
very  rapid.  In  this  manner  the  heat 


We  have  seen  the  atoms  or  mole- 1  of  the  Sun  is  transmitted  to  the  Earth 
cules  of  this  ether  mingled  with  the  and  made  sensible  to  us. 
atoms  and  molecules  constituting  the  The  light  of  the  Sun  is  communi- 
Sun.  Its  atoms  thus  in  contact  have  jcated  in  precisely  the  same  manner, 
imparted  to  them,  by  concussion,  the  Here  it  is  proper  to  observe  that  light, 
commotion  prevailing  among  the  like  heat,  is  no  longer  regarded  as 
atoms  of  the  Sun.  The  atoms  thus  set  i  a  substance,  but  is  admitted  to  be 
in  motion  communicate  motion  in  turn 'only  that  phenomenon  which  is  pre- 
to  their  own  neighboring  atoms  out-  sented  to  the  sentient  nerves  we  call 


ward,  these  to  their  outward  neigh- 
bors, and  so  on,  until  the  commotion 
is  transmitted  to  the  uttermost  out- 
ward limits  occupied  by  the  ether, 


optic,  by  such  an  intense  commo- 
tion among  the  constituent  parti- 
cles of  a  body  of  matter,  as  drives 
these  atoms  completely  asunder,  de- 


intersecting  in  the  path  the  planets  ;  stroying  their  cohesion,  causing  them 
Yulcan,  Mercury,  Venus,  Earth,  Mars,  j  to  separate  and  assume  their  atomic 
the  Asteroids,  Jupiter,  Saturn,  lira-  condition.  Hence,  light  is  a  phe- 
nus  and  Neptune.  At  the  Earth  the  |  nomenon  accompanying  the  phenome- 
motion  of  these  atoms  is  also  com- 1  non  which  we  call  heat,  that  is  pro- 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


27 


duced  by  a  particular  degree  of  motion 
among  atoms  in  commotion.  To 
make  this  clear,  let  us  by  any  ade- 
quate means  at  our  command  put  in 
motion  the  atoms  composing  a  bar  of 
iron  With  the  least  motion  engen- 
dered we  have  produced  some  degree 
of  that  commotion  which  the  sentient 
nerves  begin  to  recognize  as  heat,  and 
yet  the  optic  nerves  have  not  been 
able  to  appreciate  the  sensation.  We 
increase  the  motion  until  it  has  reach- 
ed that  degree  indicated  by  the  Fahr- 
enheit Scale  as  976,  when  the  merely 
sentient  nerves  are  largely  impressed 
with  the  sensation,  and  yet  the  optic 
nerves  have  not  been  sufficiently 
touched  to  respond.  Let  the  motion 
be  increased  one  degree  more,  to  977, 
and  instantly  the  optic  nerves  become 
sensible  to  the  existence  of  this  con- 
dition, and  recognize  the  phenomenon 
we  call  light.  The  body  composed 
of  the  atoms  in  commotion  is  now  be- 
coming luminous,  but  its  light  is  faint, 
being  barely  perceptible  to  the  vision. 
Run  the  motion  up  many  degrees 
more  and  the  body  becomes  intensely 
radiant.  It  is  red-hot  iron.  At  this 
stage  a  large  proportion  of  the  con- 
stituent atoms  are  being  set  free  from 
their  former  relations,  and  assume 
their  separate  atomic  condition.  A 
degree  of  commotion  analogous  to 
this  but  still  greater  has  been  attained 
in  the  Sun,  and  hence  it  is  not  only 
what  we  call  heated,  but  also  self-lu- 
minous. 

The  vibrations  of  the  undulations 
or  tremors  indicating  this  luminous 
condition  have  been  found  to  travel 
forward  185,500  English  miles  in  one 
second  of  time,  and  hence  to  pass 
from  the  Sun  to  the  Earth  in  about 
eight  minutes. 

Recent  satisfactory  experiments 
have  developed  at  least  two  facts  in 
electrical  science  which  render  a  few 
remarks  relative  to  electricity  not 
improper  here.  It  has  been  ascer- 
tained, first,  that  electricity  is  but  a 
manifestation  of  heat,  and  secondly, 
that  the  medium  which  transmits 
light  will  also  transmit  electricity. 


The  highly  agitated  condition  of  the 
Sun,  more  especially  during  the  great- 
est activity  of  the  Sun-spot  periods, 
must,  and  certainly  does  develop 
among  the  atoms  of  that  body  a  very 
high  degree  of  that  particular  com 
motion  which  we  denominate  Elec- 
tricity. This  motion  is  communi- 
cated to  the  inter-stellar  ether  in 
the  mariner  above  described,  and  by 
it  is  transmitted  to  the  atmosphere 
of  the  Earth,  and  of  all  the  other 
planets  as  well.  Hence,  it  is  not  at 
all  strange  that  there  should  be  periods 
of  electric  disturbance  in  our  atmos- 
phere which  correspond  with  the 
periods  of  the  Sun-spots,  but  on  the 
contrary  such  results  would  be  most 
natural  sequences  of  a  cause  which 
philosophy  thus  connects  with  them. 
The  Aurora  Borealis  is  also  thus  ac- 
counted for  upon  the  most  scientific 
basis. 

In  addition  to  this,  it  has  long  been 
observed  that  the  magnetic  needle  is 
subject  to  irregular  but  periodical 
changes  which  are  distinct  from  that 
regular  variation  which  occupies 
years  in  making  a  cycle,  and  these 
changes  can  now  be  philosophically 
traced  to  those  unusual  discharges  of 
electricity  from  the  Sun  through  the 
medium  of  the  inter-stellar  ether. 

§    28. THE  QUESTION  OP  THE  EXTINC- 
TION OF  THE  SUN. 

One  other  topic  will  suffice  to  close 
our  present  consideration  of  this  sub- 
ject. It  would  certainly  appear  a 
very  obvious  conclusion  to  draw  from 
the  Sun's  combustion,  that  the  body 
must  ultimately  be  consumed.  A 
few  propositions  may  dispel  the  error 
of  this  inference.  The  first  proposi- 
tion is  that  all  substances  are  inde- 
structible, and  although  matter  may 
be  changed  in  form  or  combination, 
yet  the  substance  composing  the  mat- 
ter still  remains  in  other  forms  or 
relations.  This  is  also  true  of  the 
Sun,  and  hence  that  body  could  be 
consumed  only  in  the  event  that 
when  its  matter  is  being  reduced  to 
a  gaseous  or  atomic  state,  and  thrown 


THE  SUN ;  ITS  CONSTITUTION,  ETC. 


into  the  stnrotmding  chromosphere  or  j  Then,  again,  since  it  has  oeen  de- 
atmosphere,  it  should  never  return  to  j  termined  that  heat,  light  and  elec- 
the  parent  body.  This  would  follow  tricity  are  not  substances,  we  have 


only  in  case  the  explosions  we  have 
described  as  taking  place  in  its  crust 
were  quite  constantly  sufficient  to 
project  the  ejected  matter  to  such  an 


no  evidence  of  any  continuous  emis- 
sion of  matter  from  the  Sun  beyond 
the  sphere  of  its  immediate    attrac- 
tion,  to  other  planets  or  Suns,  and 


immense  distance  that  the  power  of  hence  there  is  no  drain  upon  it  from 
attraction  for  the  Sun  would  be  only  !  such  a  source, 
equal  to  the  projectile  force,  which  I 


becomes  tangential,  in  which  event 
the  matter  would  not  return  to  the 
parent  body,  but  revolve  in  a  circle 
which  returns  into  itself;  or  if  the 
matter  were  projected  to  such  a  dis- 
tance and  in  such  direction  as  to 
intercept  the  stronger,  because  the 
more  immediate,  attraction  of  some 


We  have  seen  that  nearly  all,  if 
indeed  not  all,  the  matter  which  is 
ejected  from  the  Sun  through  the 
Sun  spots  by  explosions,  or  from  its 
surface  by  radiation  in  the  process  of 
reduction,*  enters  into  the  atmos- 
phere where  in  its  separate  atomic 
state  it  is  cooled  off,  thereby  becom  • 
ing  again  subject  to  the  power  of 


other  body,  and  be  thus  absorbed  by  j  attraction,  and  by  this  force   is   re- 
it.     That  the  matter  which  forms  all !  turned  to  the  photosphere  where  it 
the  planets  of  this  system  may  have 
been    so  ejected  at  different  periods 
of  time,  Mercury  and  Vulcan  at  com- 
paratively recent  periods,  is  not  im- 
possible nor  even   improbable ;    but 
even   if  this  be  true,  it  furnishes  no 


resumes  the  process  of  condensation 
on  the  exterior  and  reduction  in  the 
interior  of  that  bodv,  BO  that  no  mat- 
ter  is  lost  from  the  Sun  by  this  pro- 


cess. 


While,  however,  it  is  manifest  that 
evidence  of  an  ultimate  destruction  of  j  the  matter  of  the  Sun  will  never  be 
that  manner,  as  the  Sun  yet  contains  exhausted,  it  is  quite  as  manifest  that 


six  hundred  and  ninety-eight  seven- 
hundredths  of  all  the  matter  in  the 
Solar  Universe,  and  its  explosive 
power  must  have  so  greatly  declined 
since  the  period  when  even  the  Earth 
was  thrown  off,  that  it  will  never  be 
able  to  eject  the  immense  percentage 
of  matter  which  remains. 

It  may  be  possible,  and,  indeed, 
some  scientists  maintain  it  as  proba- 
ble, that  pome  matter  is  ejected  from 
the  Sun  by  these  explosions  with 
such  force  and  in  such  forms  that  it 
reaches  the  Earth  as  well  as  other 
planets  in  the  condition  we  call 
comets  and  meteoroids,  and  as  such 
is  absorbed.  Yet  even  if  this  be  also 
true,  it  furnishes  no  evidence  of  a 
final  extinction  of  the  Sun,  for  the 
reason  that  notwithstanding  both 
these  processes  have  been  carried  on 
for  millions  of  years,  yet  but  two 
seven  hundredths  of  the  matter  has 
been  discharged,  and  evidences  of 
decreasing  explosive  power  are  rapid- 
ly multiplying. 


the  time  will  come  when  the  conden- 
sation of  the  matter  forming  its  crust 
will  so  far  outstrip  the  process  of  re- 
duction within,  that  the  atoms  of  this 
crust  will  be  in  such  a  state  of  com- 
parative quietude  as  to  be  not  only 
no  longer  self-luminous,  but  that  thii 
quietude  will  become  so  complete  that 
the  body  will  no  longer  send  forth  its 
volume  of  heat,  but  be  as  cold  as  the 
earth,  and  as  dead,  as  regards  both 
light  and  heat,  as  is  now  the  lifeless 
moon.  Prof.  Young  estimates  that 
the  Sun  has  been  thirty  millions  of 
years  reaching  its  present  condition, 
and  that  ten  millions  of  years  will 
elapse  ere  its  light  and  heat  are  en- 
tirely extinct. 


*  It  is  the  vibratory  motion  of  the  heated 
matter  emanating  from  the  surface  of  the 
Sun,  through  the  process  of  radiation,  reduc- 
tion, or  vaporization,  as  may  be  observed  in 
a  highly  heated  mass  of  iron,  that  gives  to 
the  photosphere  the  "mottled"  appearance 
described  by  observers. 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


APPENDIX. 


1. — THE   SUN'S   CORONA  AND  HIS  SPOTS. 

(By  Richard  A.  Proctor.)* 

One  of  the  most  important  results 
of  observations  made  upon  the  eclipse 
of  July  29,  1878,  indicates  the  exist- 
ence of  a  law  of  sympathy,  so  to 
speak,  between  the  solar  corona  and 
the  Sun-spots.  The  inquiry  into  this 
relation  &eems  to  me  likely  to  lead  to 
R  very  interesting  series  of  researches, 
from  which  may  possibly  result  an 
interpretation  not  only  of  the  rela- 
tion itself,  should  it  be  found  really  to 
exist,  but  of  the  mystery  of  the  Sun- 
spot  period.  I  speak  of  the  Sun- 
spot  period  as  mysterious,  because 
even  if  we  admit  (which  I  think  we 
cannot  do)  that  the  Sun-spots  are 
produced  in  some  way  by  the  action 
of  the  planets  upon  the  Sun,  it  would 
still  remain  altogether  a  mystery  how 
this  action  operated.  When  all  the 
known  facts  respecting  the  San-spots 
are  carefully  considered,  no  theory  yet 
advanced  respecting  them  seems  at  all 
satisfactory,  while  no  approach  even 
has  been  made  to  an  explanation  of 
their  periodic  increase  and  diminution 
in  number.  This  seems  to  me  one  of 
the  most  interesting  problems  which 
astronomers  have  at  present  to  deal 
with;  nor  do  I  despair  of  seeing  it 
satisfactorily  solved  within  no  very 
long  interval  of  time.  Should  the  rec- 
ognition of  a  sympathy  between  the 
corona  and  the  Sun-spots  be  satisfac- 
torily established,  an  important  step 
in  advance  will  have  been  made, — 
possibly  even  the  key  to  the  enigma 
will  be  found  to  have  been  dis- 
covered. 

I  propose  now  to  consider,  first, 
whether  the  evidence  we  have  on  this 
subject  is  sufficient,  and  afterward  to 
discuss  some  of  the  ideas  suggested 
by  the  relations  which  have  been  rec- 
ognized as  existing  between  the  Sun- 


*  From  his  collection  of   Essays  entitled 
Rough  Ways  Made  Smooth." 


spots,  the  sierra,  the  colored  promi- 
nences, and  the  zodiacal  light. 

The  evidence  from  the  recent  eclip- 
ses indicates  beyond  all  possibility  of 
doubt  or  question,  that  during  the 
years  when  Sun-spots  were  numerous, 
m  1870  and  1871,  the  corona,  at  least 
on  the  days  of  the  total  §olar  eclipses 
in  those  years,  presented  an  appear- 
ance entirely  different  from  the  coro- 
na seen  on  July  29,  1878,  when  the 
Sun  was  almost  free  from  spots.  This 
will  be  more  fully  indicated  further 
on.     At  present  it  is  necessary  to  no- 
tice only  (1)  that  whereas  in  1870  and 
1871  the  inner  corona  extended    at 
least  250,000  miles  from  the  Sun,  it 
reached  only  to  a  height  of  some  70,-  . 
000  miles  in  1878;  (2)  in  1870  and 
1871  it  possessed  a  very  complicated 
structure,  whereas  in  1878  the  definite 
structure  could  be  recognized  only  in 
two  parts  of  the  inner  corona;  (3)  in 
1871  the  corona  was  pink,  whereas  in 
1878  it  was  pearly  white;  (4)  the  co- 
rona was  ten  times  bnghter  in  1871 
than  in  1878;  lastly,  in  1871  the  light 
f  the  corona  came  in  part  from  glow- 
ng  gas,  whereas  in  July,  1878,  the 
ight  came  chiefly,  if  not  wholly,  from. 
Rowing  solid  or  liquid  matter.   I  must 
icre  point  out,  that  the  evidence  of 
change,  however  satisfactory  in  itself, 
,vould  be  quite  insufficient   to    estab- 
ish  the  general  theory  that  the  corona 
sympathizes     with  the   solar  photo- 
phere  in  the  special  manner  suggested 
:>y    the  recent  eclipse  observations. 
There  are  few  practices  more  unscien- 
tific, or  more  likely  to  lead  to  erro- 
neous theorizing,  than  that  of  basing 
general  theory  on  a  small  number 
of    observations.     In  this  case    we 
have,  in  fact,   but  a  single  observed 
correspondence,   though    the    obser- 
vations establishing  it  form   a  series. 
It  has  been  shown  that  so  far  as  the 
special  Sun-spot  period  from  the  min- 
imum of  1 867  to  the  minimum  of  1878 
is  concerned,  there  has  been  a  certain 
correspondence  between  the  aspect  of 
the  corona  and  the  state  of  the  Sun's 
surface,  with  regard    to  spots.     To 
assume   from  that  single  correspond- 


30 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


ence  that  the  corona  and  Sun-spots  I  that  my  purpose  is  to  ascertain  where 
are  related  in  the  r:mie  way,  would  be  j  the  truth  lies.  I  shall  neither  iutro- 
hazardous  in  the  extreme.  We  may  duce  any  observation  of  the  corona, 
indeed  find,  when  we  consider  other  |  because  it  seems  specially  favorable 
matters,  that  the  probability  of  a  gen-  j  to  the  theory  that  the  corona  sympa- 
eral  relation  of  this  sort  existing  is  so  I  thizes  with  the  photosphere,  nor  omit 
great  antecedently,  that  but  slight  any,  because  it  seems  definitely  op- 


direct  evidence  would  be  required  to 
establish  the  existence  of  the  re- 
lation. But  it  must  be  remembered 
that  before  the  eclipse  of  1878  was 
observed,  with  the  special  result  I 


posed   to    that    theory.     To    prevent 
any  possibility  of  being  unconscious 
ly  prejudiced,  I  shall  take  a  series  of 
coronal    observations     collected     to- 
gether by  myself,  on  account  of  their 


have  noticed,  few  were  bold  enough  |  intrinsic   interest,  several  years  ago, 


to  assert  the  probable  existence  of 
any  such  relationship  ;  and  certainly 
no  one  asserted  that  the  probability 
was  very  strong.  I  believe,  indeed, 
that  no  one  spoke  more  definitely  in 
favor  of  the  theory  that  the  corona 
probably  sympathizes  with  the  Sun- 
spots  than  1  did  myself  before  the 
recent  eclipse ;  but  certainly  I  should 
not  then  have  been  willing  to  say  that 
I  considered  the  evidence  very  strong. 

We  must  then  look  for  evidence  of 
a  more  satisfactory  kind. 

Now,  although  dining  the  two  cen- 
turies preceding  the  invention  of  the 
spectroscope  and  the  initiation  of  the 
solar  physical  researches  now  in  pro- 
gress, observations  of  eclipses  were 
not  very  carefully  conducted,  yet  we 
have  some  records  of  the  appearance 
of  the  corona  on  different  occasions, 
which,  combined  with  the  known  law 
of  Sun  spot  periodicity,  may  enable  us 
to  generalize  more  safely  than  we 
could  from  observations  during  the 
present  spot  period,  though  these  ob- 
servations have  been  far  more  ex- 
act than  the  older  one-;.  I  propose 
to  examine  some  of  these.  Neces- 
sarily I  must  make  some  selection. 
I  need  hardly  say  that  even  if  there 
were  no  such  relation  as  that  which 
seems  to  be  indicated  by  recent  ob- 
servations, and  if  my  purpose  were 
simply  to  prove,  either  that  such  a 
relation  exists  or  that  it  does  not,  I 
could  very  readily  bring  before  the 
reader  of  these  pages  what  would 
seem  like  the  most  satisfactory  evi- 
dence that  the  relation  is  real.  I 
must  ask  him  to  believe,  however, 


when  I  had  not  in  my  thoughts  any 
theory  respecting  periodic  changes  in 
the  corona — the  series,  namely,  which 
is  included  in  the  sixth  chapter  of  my 
treatise  on  the  Sun.  Each  of  these 
observations  I  shall  consider  in  con- 
nection with  the  known  condition  of 
the  Sun  as  to  spots,  and  those  results 
which  seem  to  bear  clearly^  whether 
favorably  or  unfavorably,  on  the  the- 
ory we  "are  inquiring  into,  I  shall 
bring  before  the  reader. 

Kepler,  whose  attention  had  been 
specially  drawn  to  the  subject  of  the 
light  seen  around  the  Sun  during  to- 
tal eclipse,  by  certain  statements 
which  Clavius  had  made  respecting 
the  eclipse  of  1567,  describes  the 
eclipse  of  1605  in  the  following 
terms: — "The  whole  body  of  the 
Sun  was  completely  covered  for  a 
short  time,  but  around  it  there  shone 
a  brilliant  light  of  a  reddish  hue  and 
uniform  breadth,  which  occupied  a 
considerable  portion  of  the  heavens." 
The  corona  thus  seen  may  fairly  be 
assumed  to  have  resembled  in  extent 
that  of  1871.  A  bright  corona,  reach- 
ing like  that  seen  during  the  eclipse 
of  July,  1878,  to  a  height  of  only 
about  70,000  miles  from  the  Sun's 
surface,  would  certainly  not  have 
been  described  by  Kepler  as  occupy- 
ing a  considerable  portion  of  the 
heavens,  for  a  height  of  70,000  miles 
would  correspond  only  to  about  a 
twelfth  of  the  Sun's  diameter  ;  and  a 
ring  so  narrow  would  be  described 
very  differently.  It  seems,  then,  that 
in  1605  a  corona  was  seen  which  cor- 
responded with  that  observed  when 


THE  SUN;  ITS   CONSTITUTION,  ETC 


31 


the  Sun  has  had  many  spots  on  his 
surface.  Now  we  have  no  record  of 
the  condition  of  the  Sun  with  regard 
to  spots  in  1605  ;  but  we  know  that 
the  year  1615  was  one  of  many  spots, 
and  the  year  1610  one  of  few  spots  ; 
whence  we  may  conclude  safely 
that  the  year  1605  was  one  of  many 
spots.  This  case  then  is  in  favor  of 
the  theory  we  are  examining. 

In  passing  we  may  ask  whether  the 
observation  by  Clavius  which  had 
perplexed  Kepler,  may  not  throw 
some  light  on  our  subject.  Clavius 
says  that  the  eclipse  of  1567,  which 
should  have  been  total,  was  annular. 
The  usual  explanation  of  this  has 
been  that  the  corona  was  intensely 
bright  close  to  the  Sun.  And  though 
Kepler  considered  that  his  own  ob 
servation  of  a  broad  reddish  corona 
satisfactorily  removed  Clavius' s  dif- 
ficulty, it  seems  tolerably  clear  that 
the  corona  seen  by  Clavius  must  have 
been  very  unlike  the  corona  seen  by 
Kepler.  In  fact,  the  former  must 
have  been  like  the  corona  seen  in 
July,  1878,  much  smaller  than  the 
average,  but  correspondingly  in- 
creased in  luster.  Now  with  regard 
to  the  Sun-spot  period  we  can  go  back 
to  the  yeir  1567,  though  not  quite  so 
securely  as  we  could  wish.  Taking 
the  average  Sun-spot  period  at  eleven 
years,  and  calculating  back  from  the 
minimum  of  spots  in  the  year  1610, 
we  get  four  years  of  minimum  solar 
disturbance,  1599,  1588,  1577,  and 
1566.  We  should  have  obtained  the 
same  result  if  we  had  used  the  more 
exact  period,  eleven  one  ninth  years, 
and  had  taken  1610.8  for  the  epoch 
of  least  solar  disturbance  (1610.8 
meaning  about  the  middle  of  Octo 
ber,  1610).  Thus  the  year  1567  was 
a  year  of  few  Sun-spots,  probably  oc- 
cupying almost  exactly  the  same  po- 
sition in  the  Sun-spot  period  as  the 
year  1878.  Clavius's  observation, 
then,  is  in  favor  of  our  theory. 

But  another  observation  between 
Clavius's  and  Kepler's  may  here  be 
noticed.  Jensenius,  who  observed 
the  eclipse  of  1598  at  Torgau  in  Ger- 


many, noticed  that,  at  the  time  of 
mid- totality,  a  bright  light  shone 
round  the  moon.  On  this  occasion, 
remarks  Grant,  the  phenomenon  was 
generally  supposed  to  arise  from  a  de- 
fect in  the  totality  of  the  eclipse, though 
Kepler  strenuously  contended  that 
such  an  explanation  was  at  variance 
with  the  relation  between  the  values  of 
the  apparent  diameters  of  the  Sun 
and  Moon  as  computed  for  the  time 
of  the  eclipse  by  aid  of  the  solar  and 
lunar  tables.  The  corona,  then,  must 
have  resembled  that  seen  by  Clavius, 
and  since  the  year  1598  must  have 
been  very  near  the  time  of  fewest 
spots,  this  observation  accords  with 
the  theory  we  are  examining. 

The  next  observation  is  that  made 
by  Wyberd  during  the  eclipse  of 
1H52.  Here,  there  is  a  difficulty 
arising  from  the  strange  way  in 
which  the  Sun-spots  behave  1  during 
the  interval  from  1645  to  1679.  Ac- 
cording to  M.  Wolf,  whose  investi- 
gation of  the  subject  has  been  very 
lose  and  searching,  there  wa^  a  max- 
imum of  Sm  spots  in  1639  followed 
by  a  minimum  in  1645,  the  usual  in- 
terval of  about  six  years  having 
elapsed ;  but  there  came  a  maximum 
in  1655,  ten  years  later,  followed  by  a 
minimum  in  1666,  eleven  years  later, 
so  that  actually  twenty-one  years 
would  seem  to  have  elapsed  be- 
tween successive  minima  (1645  and 
1666).  Then  came  a  maximum  in 
1675,  nine  years  later,  and  a  mini- 
mum in  1679,  four  years  later.  Be- 
tween the  maxima  of  1639  and  1675, 
including  two  spot  periods,  an  inter- 
val of  thirty-six  years  elapsed  There 
is  no  other  instance  on  record,  so  far 
as  I  know,  of  so  long  an  interval  as 
this  for  two  spot-periods.  In  pass- 
ing, I  would  notice  how  little  this 
circumstance  accords  with  tho  theory 
that  the  Sun-spots  follow  an  exact 
law,  or  that  from  observations  of  the 
Sun,  means  can  ever  be  found  for 
forming  a  trustworthy  system  of 
weather  prediction,  even  if  we  as- 
sumed (which  has  always  seemed  to 
me  a  very  daring  assumption),  that 


32 


THE   SUN;   ITS   CONSTITUTION,  ETC. 


terrestrial  weather  is  directly  depend- 
ent on  the  progress  of  the  Sun-spot 
period.  But  here  the  irregularity  of 
the  spot  changes  affects  us  only  as 
preventing  us  from  determining  or 
even  from  guessing  what  may  have 
been  the  condition  of  the  Sun's  surface 
in  the  year  1652.  This  year  followed 
by  seven  years  a  period  of  minimum 
disturbance,  and  preceded  by  three 
years  a  period  of  maximum  disturb- 
ance ;  but  it  would  be  unsafe  to  as- 
sume that  the  Sun's  condition  in  1652 
was  nearer  that  of  maximum  than 
that  of  minimum  disturbance.  We 
must  pass  over  Wyberd's  observa- 
tions of  the  corona  in  1652,  a*  least 
until  seme  direct  evidence  as  to  the 
Sun's  condition  shall  have  been  ob- 
tained from  the  papers  or  writings  of 
the  observers  of  that  year.  I  note 
only  that  Wyberd  saw  a  corona  of 
very  limited  extent,  having  indeed  a 
height  not  half  so  great  as  that  of 
many  prominences  which  have  been 
observed  during  recent  eclipses.  If 
the  theory  we  are  examining  should 
be  established  beyond  dispute,  we 
should  be  led  to  infer  that  the  year 
1652  was  in  reality  a  year  of  mini- 
mum solar  disturbance.  Perhaps  by 
throwing  in  such  a  minimum  between 
1645  and  1666,  with  of  course  a  cor- 
responding maximum,  the  wild  irreg- 
ularity of  the  Sun  spot  changes  be- 
tween 1645  and  1679  would  be  to 
some  degree  diminished. 

We  are  now  approaching  times 
when  more  satisfactory  observations 
were  made  upon  the  corona,  and  when 
also  we  have  more  complete  records 
of  the  aspect  of  the  Sun's  surface. 

In  1706  Plantade  andCapies  saw  a 
bright  ring  of  white  light  extending 
round  the  eclipsed  Sun  to  a  distance 
of  about  85,000  miles,  but  merging 
into  a  fainter  light,  which  extended 
no  less  than  four  degrees  from  the 
eclipsed  Sun,  fading  off  insensibly  un- 
til its  light  was  lost  in  the  obscure 
background  of  the  sky.  This  corre- 
sponds unmistakably  with  such  a  coro- 
na as  we  should  expect  only  to  see  at  a 
time  of  many  Sun-spots,  if  the  theory 


we  are  examining  is  sound.  Turning 
o  Wolf's  lisr,  we  find  that  the  year 
1705  is  marked  as  a  year  of  maximum 
solar  disturbance,  and  the  year  1712 
as  that  of  the  next  minimum.  There- 
Pore  1706  was  a  year  of  many  Sun- 
spots — in  fact,  1706  may  have  been 
the  year  of  actual  maximum  disturb- 
ance, for  it  is  within  the  limits  of 
doubt  indicated  by  Wolf.  Certainly 
a  corona  extending  so  far  as  that 
which  Plantade  and  Capiessaw  would 
imply  an  altogether  exceptional  de- 
gree of  solar  disturbance,  if  the  theory 
we  are  considering  is  correct. 

In  1715  Halley  gave  the  following 
description  of  the  corona:  "A  few 
seconds  before  the  Sun  was  all  hid, 
there  discovered  itself  round  the 
Moon  a  luminous  ring  about  a  digit v 
(a  twelfth)  "or  perhaps  a  tenth  part 
of  the  Moon's  diameter  in  breadth. 
It  was  of  a  pale  whiteness  or  rather 
pearl  color,  seeming  to  me  a  little 
tinged  with  the  colors  of  the  Iris,  and 
to  be  concentric  with  the  Moon."  He 
added  that  the  ring  appeared  much 
whiter  and  brighter  near  the  body  of 
the  Moon  than  at  a  distance  from  it. 
and  that  its  exterior  boundary  was 
very  ill-defined,  seeming  to  be  deter- 
mined only  by  the  extreme  rarity  of 
the  luminous  matter.  The  French  as- 
tronomer Louville  gave  a  similar  ac- 
count of  the  appearance  of  the  ring. 
He  added,  however,  that  "there  were 
interruptions  in  its  brightness,  causing 
it  to  resemble  the  radial  glory  with 
which  painters  encircle  the  heads  of 
the  saints."  The  smallness  of  the  co- 
rona on  this  occasion  corresponds  with 
the  description  of  the  corona  Rteii  in 
July,  1878 ;  and  though  Louville's  de- 
scription of  gaps  is  suggestive  of  a 
somewhat  different  aspect,  yet,  on  the 
whole,  the  corona  seen  in  1715  more 
closely  resembles  one  which  would  be 
seen  at  a  time  of  minimum  solar  dis- 
turbance, if  our  theory  can  be  trusted, 
than  one  which  would  be  seen  at  a 
time  of  maximum  disturbance.  Wolfs 
list  puts  the  year  1712  as  one  of  min- 
imum disturbance,  with  one  year  of 
doubt  either  way,  and  the  middle  of 


THE  SUN ;  ITS  CONSTITUTION,  ETC. 


the  year  1817  as  the  epoch  of  maxi- 
mum disturbance,  with  a  similar  range 
of  uncertainty.  The  case,  then,  is 
doubtful,  but  on  the  whole  inclines  to 
being  unfavorable.  I  may  remark 
that  because  of  its  unfavorable  nature, 
I  depar  ed  from  the  rule  I  had  set  my- 
self, of  taking  only  the  cases  included 
in  my  treatise  on  the  Sun.  For  the 
corona  of  1 7 15 is  not,r! escribed  in  that 
treatise,  as  indeed  affording  no  evi- 
dence respecting  this  solar  appendage. 
The  evidence  given  in  this  case  isprob- 
ably  affected  in  some  degree  by  the 
unfavorable  atmospheric  conditions 
under  which  Halley  certainly,  and 
Louville  probably,  observed  the 
eclipse.  In  any  case  the  evidence  is 
not  ptiong;  only  I  would  call  atten- 
tion here  to  the  circumstance  that  if, 
as  we  proceed,  we  should  come  to  a 
case  iu  which  the  evidence  is  plainly 
against  the  theory  we  are  examining, 
we  must  give  up  the  theory  at  once. 
For  one  case  of  discordance  does  more 
to  destroy  a  theory  respecting  associ- 
ation between  such  and  such  phe- 
nomena, than  a  hundred  cases  of 
agreement  would  do  iu  the  way  of 
confirming  it. 

In  1724,  Maraldi  noticed  that  the 
corona  was  broadest  first  on  the  side 
toward  which  the  Moon  was  advanc- 
ing, and  afterward  on  the  side  which 
the  Moon  was  leaving.  From  this  we 
may  infer  that  the  corona  was  only  a 
narrow  ring  on  that  occasion,  since 
otherwise  the  slight  difference  of 
breadth  due  to  the  Moon's  eccentric 
position  at  the  beginning  and  end  of 
totality  would  not  have  been  notice- 
able. Now,  the  year  1723  was  one  of 
minimum  disturbance,  with  one  year 
of  doubt  either  way.  Thus  1724  was 
certainl)  a  year  of  few  Sun-spots,  and 
may  have  been  the  actual  year  of 
minimum  disturbance.  The  corona 
then  presented  an  appearance  accord- 
ing with  the  theory  we  are  consider- 
ing. 

Few  eclipses  have  been  better  ob- 
served than  that  of  the  year  1733. 
The  Royal  Society  of  Sweden  invited 
all  who  could  spare  the  time  to  assist, 


as  far  as  their  ability  permitted,  in 
recording  the  phenomena  presented 
during  totality.  The  pastor  of  Stona 
Malm  states  that  at  Catherinesholrn, 
there  was  a  ring  around  the  Sun 
about  70,OOP  miles  in  hight.  Of 
course  these  are  not  his  exact  words ; 
what  he  actually  stated  was  that  the 
ring  was  about  a  digit  in  breadth. 
This  is  the  exact  hight  assigned  to 
the  coronal  ring  by  the  observers  of 
the  eclipse  of  last  year.  The  ring 
seemed  to  be  of  a  reddish  color. 
Another  clergyman,  Vallerius,  states 
also  that  the  ring  was  of  this  color, 
but  adds  that  at  a  considerable  dis- 
tance from  the  Sun  it  had  a  greenish 
hue.  This  suggests  the  idea  that  the 
outer  corona  was  seen  also  by  Valle- 
rius, and  that  it  had  considerable 
breadth.  The  reddish  color  of  the 
inner  light  portion  would  correspond 
to  the  color  it  would  have  if  it  con- 
sisted in  the  main  of  glowing  hydro- 
gen. If  that  really  was  its  constitu- 
tion, then  the  theory  advanced  by  one 
observer  of  the  last  eclipse  that  at 
the  time  of  minimum  solar  disturb- 
ance the  glowing  hydrogen  is  with 
drawn  from  the  corona,  would  be 
shown  to  be  incorrect;  for  1733  wras 
the  actual  year  of  minimum  solar 
disturbance.  The  pastor  of  Smoland 
states  that  "during  the  total  obscura- 
tion the  edge  of  the  Moon's  disk 
resembled  gilded  brass,  and  the  faint 
ring  round  it  emitted  rays  in  an  up- 
ward as  well  as  in  a  downward  direc- 
tion, similar  to  those  seen  beneath  the 
Sun  when  a  shower  of  rain  is  impend- 
ing." The  mathematical  lecturer  of 
the  Academy  of  Charles-stadt,  M. 
Edstrom,  observed  these  rays  with 
special  attention.  He  says  that 
"they  plainly  maintained  the  same 
position  until  they  vanished  along 
with  the  ring  upon  the  re  appearance 
of  the  Sun."  On  the  other  hand,  at 
Lincopia  no  rays  were  seen.  On  the 
whole  it  seems  clear  from  the  ac- 
counts of  this  eclipse  that  the  inner 
corona  was  bright  and  narrow;  rays 
tssued  from  the  outer  faint  ring;  but 
ihey  were  very  delicate  phenomena, 


THE  SUN;   ITS  CONSTITITIION,  ETC. 


easily  concealed  by  atmospheric  haze 
and  thus  were  not  everywhere  ob- 
served. As  rays  were  seen  in  July, 
1878,  there  is  nothing  in  the  evidence 
afforded  by  the  eclipse  of  1733,  oc- 
curring at  a  time  of  fewlspots,  which 
opposes  itself  definitely  to  the  theory 
we  are  considering.  But  the  reddish 
color  of  the  corona  as  already  noticed 
is  a  doubtful  feature.  In  July,  1878, 
the  bright  inner  corona  was  of  a 
pearl  color  and  luster. 

During  the  eclipse  of  February, 
1766,  the  corona  presented  four  lu- 
minous expansions,  and  seems  to  have 
presented  a  greater  expansion  than 
•we  should  expect  in  a  year  of  mini- 
mum solar  disturbance.  Such,  how- 
ever, the  year  1766  certainly  was. 
The  evidence  in  this  case  is  unfavora- 
ble to  our  theory — not  quite  deci 
sively  so,  but  strongly.  For  we 
should  expect  that  in  the  year  of  act- 
ual minimum  disturbance  the  corona 
would  be  even  narrower  than  in  the 
year  1878,  which  was  the  year  follow- 
ing that  of  least  disturbance.  And 
again,  a  strongly  distinctive  feature 
in  the  corona  of  July,  1878,  was  the 
absence  of  wide  expansions,  such  as 
were  seen  in  1870  and  1871.  Now  if 
this  peculiarity  should  really  be  at- 
tributed to  the  relation  existing  be- 
tween the  corona  and  the  Sun-spots, 
weshould  infer  that  in  1 766  the  corona 
would  have  been  still  more  markedly 
uniform  in  shape.  The  existence  of 
four  well  marked  expansions  on  that 
occasion,  forces  us  to  assume  that 
either  the  relation  referred  to  has  no 
real  existence,  or  else  that  the  corona 
may  change  from  week  to  week  as 
the  condition  of  the  Sun's  surface 
changes,  and  that  in  February,  1766, 
the  Sun  was  temporarily  disturbed, 
though  the  year,  as  a  whole,  was  one 
of  minimum  disturbance.  But  as  the 
epoch  of  actual  minimum  was  the 
middle  of  176C,  February  1766  should 
have  been  a  time  of  very  slight  dis- 
turbance. I  do  not  know  of  any  ob- 
servations of  the  Sun  recorded  for  the  ' 
month  of  February,  1766.  On  the  j 
whole,  the  eclipse  of  1766  must  be  j 


regarded  as  throwing  grave  doubt  on 
the  relation  assumed  by  our  theory  as 
existing  between  the  corona  and  the 
Sun-spots ;  and  as  tending  to  suggest 
that  some  wider  law  must  be  in 
question  than  the  one  we  have  been 
considering — if  any  association  really 
exists. 

The  account  given  by  Don  An- 
tonio d'Ulloa  of  the  appearance  pre- 
sented by  the  corona  during  the  total 
eclipse  of  1778,  is  rendered  doubtful 
by  his  reference  to  an  apparent  rota- 
tory motion  of  the  normal  rays.  lie 
says  that  about  five  or  six  seconds 
after  totality  had  begun,  a  brilliant 
luminous  ring  was  seen  around  the 
dark  body  of  the  Moon.  The  ring 
became  brighter  as  the  middle  of  to- 
tality approached.  "  About  the  mid- 
dle of  the  eclipse,  the  breadth  of  the 
ring  was  equal  to  about  a  sixth  of 
the  Moon's  diameter.  There  seemed 
to  issue  from  it  a  great  number  of 
rays  of  unequal  length,  which  could 
be  discerned  to  a  distance  equal  to 
the  Moon's  diameter."  Then  comes 
the  part  of  d'Ulloa's  description 
which  seems  difficult  to  accept.  '  He 
says  that  ihe  corona  "  seem etj  to  be 
endued  with  a  rapid  rotatory  motion, 
which  caused  it  to  resemble  a  fire- 
work turning  round  its  center."  The 
color  of  the  light,  he  proceeds,  '*  was 
not  uniform  throughout  the  whole 
breadth  of  the  ring.  Toward  the 
margin  of  the  Moon's  di  k  it  appeared 
of  a  reddish  hue;  then  it  changed  to  a 
pale  yellow,  and  from  the  middle  to 
the  outer  border,  the  yellow  gradually 
became  fainter,  until  at  length  it 
seemed  almost  quite  white."  Setting 
aside  the  rays  and  their  rotation, 
d'Ulloa's  account  of  the  inner  corona 
may  be  accepted  as  satisfactory.  The 
hight  of  this  ring  was,  it  seems, 
about  140,003  miles,  or  twice  that  of 
the  ring  seen  in  July  1878.  As  the 
year  1779  was  one  of  maximum  solar 
disturbance,  there  were  doubtless 
many  spots  in  1778;  and  the  aspect 
of  the  corona  accorded  well  with  the 
theory  that  the  corona  expands  as  the 
number  of  Sun-spots  increases. 


THE   SUN ;  .ITS  CONSTITUTION,  ETC. 


We  come  now  to  three  eclipses 
which  are  especially  interesting  as 
having  been  all  carefully  observed, 
some  observers  having  seen  all 
three, — the  eclipses,  namely,  of  1842, 
1851,  and  1860.  Unfortunately,  the 
eclipses  of  1842  and  1851,  occurred 
when  the  Sun-spots  were  neither  at 
their  greatest  nor  at  their  least  degree 
of  frequency.  For  a  maximum  of 
Sun-spots  occurred  in  1837,  and  a  min- 
imum in  1844,  so  that  1842  was  on 
what  may  be  called  the  descending 
slope  of  a  Sun-spot  wave,  nearer 
the  hollow  than  the  crest,  but 
riot  very  near  either:  again,  a 
maximum  occurred  in  1848,  and  a 
minimum  in  1856,  so  that  1851  was 
also  on  the  descending  slope  of  a  Sun 
spot  wave,  rather  nearer  the  crest 
than  the  hollow,  but  one  may  fairly 
say  about  midway  between  them. 
Still  it  is  essential  in  an  inquiry  of 
this  sort  to  consider  intermediate 
cases.  We  must  not  only  apply  the 
comparentia  ad  intellectum  instartti- 
arum  convenient  ium,  but  also  the 
comparentia  instant  iarum  secundum 
magis  ac  minus.  If  the  existence  of 
great  solar  disturbances  causes  the 
corona  to  be  greatly  enlarged,  as  com- 
pared with  the  corona  seen  when  the 
Sun  shows  no  spots,  we  should  expect 
to  find  the  corona  moderately  en- 
larged only  when  the  Sun  shows  a 
considerable  but  not  the  maximum 
number  of  spots.  And  again,  it  is 
conceivable  that  we  may  tiiid  some 
noteworthy  difference  between  the 
aspect  of  the  corona  when  Sun-spots 
are  diminishing  in  number,  and  its 
aspect  when  they  are  increasing. 
This  point  seems  the  more  to  need  in- 
vestigation when  we  note  that  the 
evidence  derived  from  eclipses  occur- 
ring near  the  time  either  of  maximum 
or  of  minimum  solar  disturbance  has 
not  been  altogether  satisfactory.  It 
may  be  that  we  may  find  an  explana- 
tion of  the  discrepancies  we  have  re- 
cognized, in  some  distinction  between 
the  state  of  the  corona  when  spots  are 
increasing  and  when  they  are  dimin- 
ishing in  number. 


It  is  noteworthy  that  several  care- 
ful observers  of  the  corona  in  1842 
believed  that  they  could  recognize 
motion  in  the  coronal  rays.  Francis 
Bail 7  compared  the  appearance  .of 
tho  corona  to  the  flickering  light 
of  a  gas  illumination.  O.  Struve 
also  was  much  struck  by  the  appear- 
ance of  violent  agitation  in  the  light 
of  the  ring.  It  seems  probable  that 
the  appearance  was  due  to  move- 
ments in  that  part  of  our  atmosphere 
through  which  the  corona  was  ob- 
served. The  extent  of  the  corona 
was  variously  estimated  by  different 
observers.  Petit,  at  Montpeliei,  as- 
signed to  it  a  breadth  corresponding 
to  a  highth  of  about  200  OOJ  miles; 
Baily  a  hight  of  about  509,030  miles; 
and  O.  Struve  a  eight  of  more  than 
800.000  miles.  The  last-named  ob- 
server also  recognized  luminous  ex- 
pansions extending  fully  four  degrees 
(corresponding  to  nearly  seven  million 
miles)  from  the  Sun.  Picozzi,  at  Mi- 
lan, noticed  two  jets  of  light,  which 
were  seen  also  by  observers  in  France. 
Rays  also  were  seen  by  Mauvais  at 
Perpignan,  and  by  Baily  at  Paria. 
But  Airy,  observing  the  corona  from 
the  Superga,  could  see  no  radiation. 
He  says  "although  a  slight  radiation 
might  have  been  perceptible,  it  was 
not  sufficiently  intense  to  affect  in  a 
sensible  degree  the  annular  structure 
by  which  the  luminous  appearance 
was  plainly  distinguished."  These 
varieties  in  the  aspect  of  the  corona 
were  doubtless  due  to  varieties  in  the 
condition  of  the  atmosphere  through 
which  the  corona  was  seen.  Now  it 
cannot  be  questioned  that,  so  far  as 
extension  is  concerned,  the  corona 
seen  in  1842  was  one  which,  if  the 
theory  we  are  considering  were  sound, 
we  should  expect  to  see  near  the  time 
of  maximum  rather  than  of  minimum 
solar  disturbance.  On  the  other  hand, 
in  brightness  the  corona  of  1842,  re- 
sembled, if  it  did  not  surpass,  that  of 
July  1878. 

UI  had  imagined,"  says  Baily, "that 
the  corona,  as  to  its  brilliant  or  lumin- 
ous appearance,  would  not  be  greater 


36 


THE  SUK;  ITS  CONSTITUTION,  ETC. 


than  that  faint  crepuscular  light  which 
sometimes  takes  place  (sic)  in  a  sum- 
mer evening,  and  that  it  would  encir- 
cle the  Moon  like  a  ring.  I  was  there- 
fore somewhat  surprised  and  aston- 
ished at  the  splendid  scene  which  now 
BO  suddenly  burst  upon  my  view." 

The  light  of  the  corona  was  so 
bright,  O.  Struve  states,  that  the 
naked  eye  could  scarcely  endure  it; 
"many  could  not  believe,  indeed,  that 
the  eclipse  was  total,  so  strongly  did 
the  corona's  light  resemble  direct  sun- 
light." Thus  while  as  to  extent  the 
corona  in  1842  presented  the  appear- 
ance to  be  exnected  at  the  time  of 
maximum  solar  disturbance,  if  our 
theory  is  sound,  its  brightness  was 
that  corresponding  to  a  time  of  mini- 
mum disturbance.  Its  structure  cor- 
responded with  the  former  condition. 
The  light  of  the  corona  was  not  uni- 
form, nor  merely  marked  by  radia- 
tions, but  in  several  places  interlacing 
lines  of  light  could  be  seen.  Arago, 
at  Perpignan,  observed  with  the  un- 
aided eye  a  region  of  the  corona 
where  the  structure  was  as  of  inter- 
twined jets  giving  an  appearance 
reppinbling  a  hank  of  thread  in  dis- 
order. 

Certainly,  for  an  eclipse  occurring 
two  years  from  the  time  of  minimum, 
and  live  years  from  the  time  of  maxi- 
mum disturbance,  that  of  July,  1842,* 
has  not  supplied  evidence  favoring 
the  theory  with  which  we  started. 
Whether  any  other  theory  of  asso- 
ciation between  the  corona  and  the 
Sun- spots  will  better  accord  with  the 


*  1  he  actual  condition  of  the  .**un  in  1842 
may  be  infeired  from  the  following  table, 
showing  the  number  of  spots  observed  in 
1837  the  preceding  year  of  maximum  dis- 
turbance, in  184U,  and  in  1844  the  following 
year  of  minimum  disturbance  ;  the  observer 
\vas  fcchwabe  of  Dessau  : 

Days  of      Days  without    New  groups 
obst  rvation.         spots.  obst  rvtd. 

1837    .    168  0  333 

1842    .    307  64  68 

1844    .321  111  62 

Only  it  should  be  noticed  that  nearly  all  the 
spots  seen  in  the  year  1844  belonged  to  the 
next  period,  the  time  of  actual  minimum  oc- 
curring earlv  ;n  1844. 


evidence  hitherto  collected  remains  to 
be  seen. 

Turn  we  now  to  the  eclipse  of  1851, 
occurring  nearly  midway  between  the 
epoch-  of  maximum  solar  disturbance 
(1848)  and  minimum  solar  disturb- 
ance (1856).  I  take  the  account  given 
by  Airy,  our  government  astronomer, 
as  he  was  one  of  the  observers  of  the 
eclipse  of  1842. 

"  The  corona  was  far  broader,"  he 
says,  "than  that  which  I  saw  in  1842. 
Roughly  speaking,  the  breadth  was 
little  less  than  the  Moon's  diameter, 
but  its  outline  was  very  irregular. 
I  did  not  notice  any  beams  project- 
ing from  it  which  deserved  notice  as 
much  more  conspicuous  than  the 
others;  but  the  whole  was  beamy, 
radiated  in  structure,  and  termi- 
nated— though  very  indefinitely — in 
a  way  which  reminded  me  of  the 
ornament  frequently  placed  round  ;> 
mariner's  compass.  Its  color  was 
white,  or  resembling  that  of  Venus. 
I  saw  no  flickering  or  unsteadiness  of 
light.  It  was  not  separated  fiom  the 
Moon  by  any  interval,  nor  ha  1  it  any 
annular  structure.  It  looked  like  a 
radiated  luminous  cloud  behind  the 
Moon." 

The  corona  thus  described  belongs 
to  that  which  our  theory  associates 
with  the  period  of  maximum  rather 
than  of  minimum  solar  disturbance. 
Definite  peculiarities  of  structure 
seem  to  have  been  more  numerous 
and  better  marked  than  in  1842.  It 
accords  with  our  theory  that  1851 
was  a  year  of  greater  solar  disturb- 
ance than  was  observed  in  1842,  as 
the  following  numbers  show: 

Days  of      Days  without     New  groups 
observation.        spots.  obs  rvtd. 

1842     .317  64  68 

1851     .     308  0  141 

1860    .     332  0  211 

I  have  included  the  year  1860,  as  we 
now  proceed  to  consider  the  corona 
then  seen  by  Airy.  The  year  1860 
did  not  differ  very  markedly,  it  will 
be  observed,  from  1851,  at  regards 
the  number  of  new  groups  af  spots 
observed  by  Schwabe,  especially  when 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


37 


account  is  taken  of  the  number  of 
days  in  which  the  Sun  was  observed 
in  these  two  years.  But  1 860  was  a 
year  of  maximum  solar  disturbance, 
whereas  1851  was  not.* 

Airy  rein  arks  of  the  corona  in  1860 : 
"It  gave  a  considerable  body,  but  I 
•  lid  not  remark  either  by  eye-view  or 
by  telescope  view  anything- annular 
in  its  structure ;  it  appeared  to  me  to 
resemble,  with  some  irregularities  (as 
I  stated  in  1851),  the  ornament  round 
a  compass  card." 

Bruhns  of  Leipsic  noted  that  the 
corona  shone  with  an  intense  white 
light,  so  lustrous  as  to  dim  the  pro- 
tuberances. He  noticed  that  a  ray 
shot  out  to  a  distance  of  abou^  one 
degree  indicating  a  distance  of  at 
least  1,500,000  miles  from  the  Sun's 
surface.  This  was  unquestionably  a 
coronal  appendage  as  neither  the  di- 
rection nor  the  length  of  the  ray  va- 
ried for  ten  seconds,  during  which 
Bruhns  directed  his  attention  to  it. 
Its  light  was  considerably  feebler 
than  that  of  the  corona,  which  was  of 
a  glowing  white,  and  seemed  to  co- 
ruscate or  twinkle.  Bruhns  assigned 
to  the  inner  corona  a  height  varying 
from  abont  40,000  to  about  80,000 
miles.  But  this  was  unquestionably 
far  short  of  the  true  height.  In  fact, 
Secchi's  photographs  show  the  corona 
extending  to  a  distance  of  at  least 
175,000  miles  from  the  surface  of  the 
Sun.  Therefore  probably  what 
Bruhns  calls  the  base  of  the  corona 
was  in  reality  only  the  prominence 


*  The  following  table  shows  the  position 
occupied  by  the  years  1851  and  1860  in  this 
report,  as  com  pared  with  the  year  1848  (max- 
imum next  preceding  1851),  18-fi6  (minimum 
next  following  1851)  and  1867,  minimum 
next  following  1860  : 


1848 
1851 
1856 
1860 
1867 


Days  of      Days  without 
observation.        spots. 

278 


321 
332 
312 


0 
0 

193 
0 

195 


New  groups 
observed. 
930 
141 
34 
211 
25 


A  comparison  of  the  three  tables  given  in 
these  notes  and  the  text  will  afford  some  idea 
of  the  irregularities  existing  in  the  various 
waves  of  Sun-spots. 


region,  and  the  inner  corona  was  that 
which  he  describes  as  varying  in 
breadth  or  height  from  nearly  one- 
half  to  a  quarter  of  a  degree — that  ia 
from  about  800,000  to  about  400,000 
miles.  De  la  Rue  gives  a  somewhat 
similar  general  description  of  the  co- 
rona seen  in  1 860.  Pie  remarks  that 
it  was  extremely  bright  near  the 
Moon's  body,  and  of  a  silvery  white- 
ness. The  picture  of  the  corona  by 
Feilitsch  (given  at  page  343  of  my 
book  on  the  Sun)  accords  with  these 
descriptions. 

On  the  whole,  the  eclipse  of  1860 
affords  evidence  according  well  with 
the  theory  we  have  been  considering, 
except  as  regards  the  brightness  and 
the  color  of  the  corona,  which  corres- 
pond more  closely  with  what  was 
observed  in  July,  1878,  with  the  lus- 
ter and  color  of  the  corona  in  1870 
and  1871.  In  this  respect,  it  is  sin- 
gular that  the  eclipse  of  1867,  which 
occurred  (see  preceding  note)  when 
the  Sun-spots  were  fewer  in  number, 
presented  a  decided  contrast  to  that 
of  1860, — the  contrast  being,  how- 
ever, precisely  the  reverse  of  that 
which  our  theory  would  require,  if 
the  color  and  brightness  of  the  co- 
rona be  considered  essential  features 
of  any  law  of  association. 

Herr  Grosch,  decribing  the  corona 
of  1867,  says,  "There  appeared 
around  the  Moon  a  reddish  glimmer- 
ing light  similar  to  that  of  tho  aurora, 
and  almost  simultaneously  with  this, 
(I  mean  very  shortly  after  It)  the  co- 
rona." It  is  clear,  however,  from 
what  follows,  that  tho  reddish  light 
was  what  is  now  corumonly  called 
the  inner  corona,  wnioh  in  July,  1878, 
when  the  Sun  was  m  almost  exactly 
the  same  condition  as  regards  the 
spots,  was  peariy  white  and  intensely 
bright.  "T'ais  reddish  glimmer,"  he 
proceeds,  "  which  surrounded  the 
Moon  with  a  border  of  the  breadth  of 
at  most  live  minutes  "  (about  140,000 
miles)  u  was  not  sharply  bounded  in 
any  part,  but  was  extremely  diffused 
and  less  distinct  in  the  neighborhood 
of  the  poles.''  Of  the  outer  corona, 


3ft 


THE   SUN;   ITS   CONSTITUTION,  ETC. 


he  remarks  that  "  its  apparent  height 
amounted  to  about  280,000  miles  op- 
posite the  solar  poles,  but  opposite 
the  eolar  equator  to  about  670.000 
miles.  Its  light  was  white.  This 
white  light  was  not  in  the  least  ra- 
diated itself,  but  it  had  the  appear- 
ance of  rays  penetrating  through  it ; 
or  rather  as  if  rays  ran  over  it, 
forming  symmetrical  pencils  diverg- 
ing outward,  and  passing  far  beyond 
the  boundary  of  the  white  light. 
These  rays  had  a  more  bluish  appear- 
ance, and  might  best  be  compared  to 
those  produced  by  a  great  electro- 
magnetic light.  Their  similarity  to 
these,  indeed,  was  so  striking,  that 
under  other  circumstances  I  "should 
have  taken  them  for  such,  shining  at 
a  great  distance.  The  view  of  the 
corona  I  have  described  is  that  seen 
with  the  naked  eye.  .  .  In  the 
white  light  of  the  corona,  close  upon 
the  Moon's  edge,  there  appeared  sev- 
eral dark  curves.  They  were  sym- 
metrically arched  toward  the  east 
and  west,  sharply  drawn,  and  re- 
sembling in  tint  lines  drawn  with  a 
lead  pencil  upon  white  paper.  .  . 
Beginning  at  a  distance  of  one  min 
ute  (about  26,000  miles),  they  could 
be  traced  up  to  a  distance  of  about 
nine  minutes  (some  236,000  miles) 
from  the  Moon's  edge." 

Almost  all  the  features  observed  in 
this  case  correspond  closely  with 
those  noted  and  photographed  during 
the  eclipse  of  December,  1871.  In 
other  words,  the  corona  seen  in  1867, 
when  the  Sun  was  passing  through 
the  period  of  least  solar  disturbance, 
closely  resembled  the  corona  seen  in 
J871,  when  the  Sun  was  nearly  in  its 
stage  of  greatest  disturbance.  Even 
the  spectroscopic  evidence  obtained 
in  1871  and  July,  1878,  maybe  so  ex- 
tended as  to  show  with  extre.ne 
probability  what  would  have  been 
seen  in  1867  if  spectroscopic  analysis 
had  then  been  applied.  We  cannot 
doubt  that  the  reddish  inner  corona, 
extending  to  a  height  of  about  140,000 
miles,  would  have  been  found  under 
Bpectroscopic  analysis  to  shine  in  part 


with  the  light  of  glowing  hydrogen, 
as  the  reddish  corona  of  1871  did. 
The  white  corona  of  July,  1878,  on 
the  contrary,  shone  only  with  such 
light  as  comes  from  glowing  solid  or 
liquid  matter.  Here  then,  again,  the 
evidence  is  unfavorable  to  our  theory; 
for  the  corona  in  1867  should  have 
closely  resembled  the  corona  of  1878, 
if  this  theory  were  sound. 

It  would  be  idle,  I  think,  to  seek 
for  farther  evidence  cither  in  favor 
of  the  theory  we  originally  proposed 
to  discuss,  or  against  it:  for  the  evi- 
dence of  the  eclipse  of  1867  disposes 
finally  of  the  theory  in  that  form.  I 
may  note  in  passing  that  the  eclipse 
of  1868  gave  evidence  almost  equally 
unfa'vorable  to  the  theory,  while  the 
evidence  given  by  the  eclipse  of  1869 
was  neutral.  It  will  be  desirable, 
however,  to  consider,  before  conclud- 
ing our  inquiry,  the  evidence  obtained 
in  1871  and  in  1878,  in  order  that 
we  mny  see  what,  after  all,  that  evi- 
dence may  be  regarded  as  fairly  prov- 
ing with  regard  to  coronal  variations. 

First,  however,  as  1  have  consid- 
ered t\vo  eclipses  which  occurred 
when  the  Sun  spots  were  decreasing 
in  number — namely,  thcae  of  1842 
and  1851,  midway  (roughly  speaking) 
between  the  crest  and  hollow  of  the 
Sun-spot  waveon  its  descending  slope, 
it  may  be  well  to  consider  an  eclipse 
which  was  similarly  sit-iated  with  re- 
spect to  the  ascending  slope  of  a  Sun- 
spot  wave.  I  take,  then,  the  eclipse 
of  1858,  as  seen  in  Brazil  by  Liais. 
The  picture  drawn  by  this  observer 
is  one  of  the  most  remarkable  views 
of  the  corona  ever  obtained.  It  is 
given  at  page  339  of  my  book  on  the 
Sun.  Formerly  it  was  the  custom  to 
deride  this  drawing,  but  since  the 
eclipse  of  1871,  when  the  corona  was 
photographed,  it  has  been  admitted 
that  Liais's  drawing  may  be  accepted 
as  thoroughly  trustworthy.  It  shows 
a  wonderfully  complex  corona,  like 
that  of  1871,  extending  some  700,- 
000  miles  from  the  Sun,  and  corres- 
ponding in  all  respects  with  such  a 
corona  as  our  theory  (if  established) 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


would  have  associated  with  the  stage 
of  maximum  solar  disturbance.  As 
in  this  respect  the  eclipse  of  1858, 
when  Sun  spots  were  increasing,  re- 
sembled those  of  1842  and  1851> 
when  Sun-spots  were  diminishing  in 
number,  we  find  no  trace  of  any  law 
of  association  depending  on  the  rate 
of  increase  or  diminution  of  solar 
disturbance. 

If  we  limited  our  attention  to  the 
eclipses  of  1871  and  of  July,  1878, 
we  should  unquestionably  be  led  to 
adopt  the  belief  that  the  corona  dur- 
ing a  year  of  many  spots  differs  mark- 
edly from  the  corona  when  the  Sun 
shows  few  spots,  or  none.  So  far  as 
the  aspect  of  the  corona  is  concerned, 
I  take  the  description  given  by  the 
same  observer  in  both  cases,  as  the 
comparison  is  thus  freed  as  far  as  pos- 
sible from  the  effect  of  personal  dif- 
ferences. 

Mr.  Lockyer  recognized  in  1871  a 
corona  resembling  a  star-like  decora- 
tion, with  its  rays  arranged  almost 
symmetrically — three  above  and  three 
below  two  dark  spaces  or  rifts  at  the 
extremity  of  a  horizontal  diameter. 
The  rays  were  built  up  of  innumera- 
ble bright  lines  of  different  length, 
with  more  or  less  dark  spaces  between 
them.  Near  the  Sun  this  structure 
was  lost  in  the  brightness  qf  the  cen- 
tral ring,  or  inner  corona.  In  the  tel- 
escope he  saw  thousands  of  interlac- 
ing filaments,  varying  in  intensity. 
The  rays  so  definite  to  the  eye  were 
not  seen  in  the  telescope.  The  com- 
plex structure  of  interlacing  filaments 
could  be  traced  only  to  a  height  of 
some  five  or  six  minutes  (from  135,- 
000  to  165,000  miles)  from  the  Sun, 
there  dying  out  suddenly.  The  spec- 
troscope showed  that  the  inner  co- 
rona, to  this  height  at  least  (butRespi- 
ghi's  spectroscopic  observations  prove 
the  same  for  a  much  greater  distance 
from  the  Sun),  was  formed  in  part  of 
glowing  gas — hydrogen  —  and  the 
vapor  of  some  as  yet  undetermined 
substance,  shining  with  light  of  a 
green  tint,  corresponding  to  1474  of 
Kirchhoff's  scale.  But  also  a  part  of 


the  coronal  light  came  from  matter 
which  reflected  sunlight;  for  its  spec- 
trum was  the  rainbow-tinted  streak 
crossed  by  dark  lines,  which  we  ob- 
tain from  any  object  illuminated  by 
the  Sun's  rays.  Ifc  should  be  added 
that  the  photographs  of  the  corona  in 
1871  show  the  three  great  rays  above 
and  three  below,  forming  tho  appear- 
ance as  of  a  star-like  decoration,  de- 
scribed by  Mr.  Lockyer;  insomuch  as 
it  is  rather  strange  to  find  Mr.  Lock- 
yer remarking  that  "the  difference 
between  the  photographic  and  the 
visible  corona  came  out  strongly,  .  .  .. 
and  the  non  solar  origin  of  the  radial 
structure  was  conclusively  estab- 
lished." The  resemblance  is,  indeed, 
not  indicated  in  the  rough  copy  of  the 
photographs  which  illustrates  Mr. 
Lockyer's  paper;  but  it  is  clearly 
seen  in  the  photographs  themselves, 
and  in  the  fine  engraving  which  has 
been  farmed  from  them  for  the  illus- 
tration of  the  volume  which  the  As- 
tronomical Society  proposes  to  issue 
^some  time  in  the  present  century, 
perhixps). 

Now  in  July,  1878,  the  corona  pre- 
sented an  entirely  different  appear- 
ance. Mr.  Lockyer,  in  a  telegram 
sent  to  the  J)aity  News,  describes  it 
as  small,  of  pearly  luster,  and  having 
indications  of  definite  structure  in 
two  places  only.  Several  long  rays 
were  seen  ;  but  the  inner  corona  was 
estimated  as  extending  to  a  height  of 
about  70,000  miles  from  the  Sim's 
surface.  The  most  remarkable 
change,  however,  was  that  which 
had  taken  place  in  the  character  of 
the  corona's  spectrum — or,  in  other 
words,  in  the  physical  structure  of 
the  corona.  The  bright  lines  or 
bright  images  of  the  inner  corona, 
according  as  it  was  examined  through 
a  slit  or  without  one,  were  not  seen 
in  July,  1878,  showing  that  no  part, 
or  at  least  no  appreciable  part,  of  its 
light  came  from  glowing  gaseous 
matter.  But  also  the  dark  lines  seen 
by  Janssen  in  1871  were  wanting  on 
this  occasion,  showing  that  the  corona 
did  not  shine  appreciably  by  reflect- 


40 


THE   SUN;   ITS   CONSTITUTION,  ETC. 


ing  sunlight,  The  spectrum  was,  in 
fine,  a  continuous  rainbow-tinted 
streak,  such  as  that  given  by  glowing 
solid  or  liquid  matter. 

The  inference  clearly  is,  1.  That 
in  July,  1878,  the  gaseous  matter 
which  had  been  present  in  the  corona 
in  1871  was  either  entirely  absent  or 
greatly  reduced  in  quantity;  2.  The 
particles  of  solid  or  liquid,  but,  proba- 
bly, solid  matter  which,  by  reflecting 
sunlight,  produced  a  considerable  por- 
tion of  the  corona's  light  in  1871, 
were  glowing  with  heat  in  July, 


It  remains  to  be  considered  how 
science  may  hope  to  obtain  more 
trustworthy  evidence  than  we  yet 
have  respecting  the  corona  and  its 
changes  of  form,  extent,  luster,  and 
physical  constitution.  In  the  case  of 
the  prominences,  we  have  the  means 
of  making  systematic  observations  on 
every  fine,  clear  day.  It  has  been, 
indeed,  through  observations  thus 
effected  by  the  spectroscopic  method 
that  an  association  has  been  m-o^ 
nized  between  the  number,  size,  ami 
brilliancy  of  the  prominences  on  the 


1878,  and  shone  in  the  main  with  this'one  hand,  and  the  number,  size  and 


inherent  light ;  and  8.  The  entire  co- 
rona was  greatly  reduced  in  size  in 
July,  1878,  as  compared  with  that 
which  formed  the  "starlike  decora- 
tion ' '  around  the  black  body  of  the 
Moon  in  December,  1871 

We  cannot,    however,    accept   the 

theory  that  such  a  corona  as  wasj other  time.  Of  course,  without  the 
seen  in  1871  invariably  surrounds  the  aid  of  the  spectroscope  the  corona,  as 
Sun  in  years  of  great,  disturbance, 'ordinarily  seen  during  total  eclipses. 
while  the  corona  of  July,  1873,  is  [must  be  entirely  invisible  when  the 
the  typical  corona  for  years  of  small  Sun  is  shining  in  full  splendor.  No 


activity  of  the  Sun-spots  on  the  other. 
But  in  the  case  of  the  corona  we  are 
as  yet  unable  to  make  any  observa- 
tions except  at  the  time  of  total  solar 
eclipse.  It  seems  almost  impossible 
to  hope  that  any  means  can  be  de- 


for seeincr  the  corona    at 


any 


solar  disturbance.  The  generalization 
is  flatly  contradicted  by  the  evidence 
which  I  have  presented  in  the  preced 
ing  pages.  It  may  be  that  such  a 
corona  as  was  seen  in  1871  is  com- 
mon in  years  of  great  disturbance 
just  as  spots  are  then  more  common, 
though  not  always  present;  while 
such  a  corona  as  was  seen  in  July, 
1878,  is  more  common  in  years  of 
small  disturbance,  just  as  days  when 
the  Sun  is  wholly  without  spots  are 
then  more  common,  though  from 
time  to  time  several  spots,  and  some- 
times very  large  spots,  are  seen  in 
such  years.  On  the  whole,  I  think 
the  evidence  I  have  collected  favors 
rather  strongly  the  inference  that  an 
association  of  this  sort  really  exists 
between  the  corona  and  the  Sun-spots. 
It  would,  however,  be  unsafe  at  pres- 
ent to  generalize  even  to  this  extent ; 
while  certainly  the  wide  generaliza 
tion  telegraphed  to  Europe  from 
America  as  the  great  result  of  the 
eclipse  observations  in  July,  1878, 
must  unhesitatingly  be  rejected. 


one  acquainted  with  even  the  merest 
elements  of  optics  could  hope  to  see 
the  corona  with  an  ordinary  telescope 
at  such  a  time.  The  spectroscope, 
again,  would  not  help  in  the  slight  jst 
degree  to  show  such  a  corona  as  was 
shhung  in  July,  1878;  for  the  power 
of  the  spectroscope  to  show  objects 
which  under  ordinary  conditions  are 
invisible,  depends  on  the  separation 
of  rays  of  certain  tints  from  the  rays 
of  all  the  colors  of  the  rainbow,  which 
make  up  solar  light;  and  as  the  co- 
rona in  July,  1878,  shone  with  all  the 
colors  of  the  rainbow,  and  not  with 
certain  special  tints,  the  power  of  the 
spectroscope  would  be  thrown  away 
on  a  corona  of  that  kind.  All  that 
wo  can  ever  hope  to  do  is  to  discern 
the  gaseous  corona  when,  as  in  1871, 
it  is  well  developed,  by  spectroscopic 
appliances  more  effective  for  that 
purpose  than  any  which  have  hith- 
erto been  adopted—for  all  which  have 
as  yet  been  adopted  have,  failed. 
Now,  the  difficulty  of  the  problem 
11  be  recognized  when  we  remem- 


THE   SUN;   ITS   CONSTITUTION,  ETC. 


41 


ber  that  the  strongest  tints  of  the 
corona' B  light — the  green  tint  classi- 
fied as  1474  Kirchhoff — has  been 
specialty  but  ineffectually  searched 
for  in  the  Sun's  neighborhood  with  the 
most  powerful  spectroscopic  appli 
ances  yet  employed  in  the  study  of 
the  colored  prominences.  In  other 
words,  when  the  light  of  our  own 
air  over  the  region  occupied  by  the 
corona  has  been  diluted  as  far  as  pos- 
sible by  spectroscopic  contrivances, 
the  strongest  of  the  special  coronal 
tints  has  yet  failed  to  show  through 
the  diluted  spectrum  of  the  sky. 
Again,  we  have  even  stronger  evi- 
dence of  the  difficulty  of  the  task  in 
the  spectroscopic  observations  made 
by  Respighi  during  the  eclipse  of 
1871.  The  instrument,  or  I  should 
rather,  perhaps,  say  the  arrangement, 
which  during  mid  totality  showed  the 
green  image  of  the  corona  to  a  height 
of  about  280  000  miles,  did  not  show 
any  green  ring  at  all  at  the  beginning 
of  totality.  In  other  words,  so  faint 
ia  the  light  of  the  gaseous  corona, 
even  at  its  brightest  part,  close  to  the 
Sun,  that  the  faint  residual  atmos- 
pheric light  which  illuminates  the 
sky  over  the  eclipsed  Sun  at  the  be- 
ginning of  totality  sufficed  to  oblite- 
rate this  part  of  the  coronal  light. 

Whether  with  any  combination 
specially  directed  to  meet  the  difficul- 
ties of  this  observation,  the  gaseous 
corona  can  be  rendered  discernible, 
remains  to  be  seen.  I  must  confess 
my  own  hopes  that  the  problem  will 
ever  be  successfully  dealt  with  are 
very  slight,  though  not  absolutely 
evanescent.  It  seems  to  me  barely 
possible  that  the  problem  might  be 
successfully  attacked  in  the  following 
way.  Using  a  telescope  of  small 
size,  for  the  larger  the  telescope  the 
fainter  is  the  image  (because  of  great- 
er loss  of  light  by  absorption,)  let  the 
image  of  the  Sun  be  received  in  a 
small,  perfectly  darkened  camera  at- 
tached to  the  eye-end  of  the  telescope. 
Now,  if  the  image  of  the  Sun  were 
received  on  a  smooth,  white  surface, 
we  know  that  the  prominences  and 


the  corona  would  not  be  visible. 
|  And  again,  if  the  part  of  such  a  sur- 
face on  which  the  image  of  the  Sun 
itself  fell,  were  exactly  removed,  we 
know  (the  experiment  has  been  tried 
by  Airy)  that  the  prominences  would 
not  be  seen  on  the  ring  of  white  sur- 
face left  after  such  excision.  Still 
less,  then,  would  the  much  fainter 
image  of  the  corona  be  seen.  But, 
if  'this  ring  of  white  surface,  illu 
minated  in  reality  by  the  sky,  by  the 
ring  of  prominences  and  sierra,  and 
by  the  corona,  were  examined  through 
a  battery  of  prisms  (used  without  a 
slit)  adjusted  to  any  one  of  the  known 
prominence  tints,  the  ring  of  prom- 
inences and  sierra  would  be  seen  in 
that  special  tint.  If  the  battery  .  of 
prisms  were  sufficiently  effective, 
and  the  tint  were  one  of  the  hydro- 
gen tints,  preferably,  perhaps,  the 
red — we  might  possibly  be  able  to 
trace  the  faint  image  of  the  corona 
in  that  tint.  But  we  should  have  a 
better  chance  with  the  green  tint  cor- 
responding to  the  spectral  line  1474 
Kirchhoff.  If  the  ring  of  white  sur- 
face were  replaced  by  a  ring  of  green 
surface,  the  tint  being  as  nearly  that 
of  1474  Kirchhoff  as  possible,  the 
chance  of  seeing  the  coronal  ring  in 
that  tint  would  be  somewhat  in- 
reased ;  and,  still  further,  perhaps, 
if  the  field  of  view  were  examined 
through  green  glass  of  the  same  tint. 
It  seems  just  possible  that  if  prisms 
of  triple  height  were  used,  through 
which  the  rays  were  carried  three 
times,  by  an  obvious  modification  of 
the  usual  arrangement  for  altering 
the  level  of  the  rays,  thus  giving  a 
power  of  eighteen  flint  glass  prisms 
of  ;ixty  degrees  each,  evidence, 
though  slight  perhaps,  might  be  ob- 
tained of  the  presence  of  the  sub- 
stance which  produces  the  green 
line.  Thus,  variations  in  the  con- . 
dition  of  the  corona  might  be  recog- 
nized, and  any  law  affecting  such 
variations  might  be  detected.  I  must 
confess,  however,  that  a  consider- 
ation of  the  optical  relations  involved 
n  the  problem,  leads  me  to  regard 


THE  SUN;   ITS  CONSTITUTION,  ETC. 


the  attempt  to  recognize  any  traces 
of  the  corona  when  the  Sun  is  not 
eclipsed,  as  almost  hopeless. 

It  is  clear  that  until  some  method 
for  thus  observing  the  corona  has 
been  devised,  future  eclipse  observa- 
tions will  acquire  a  now  interest  from 
the  light  which  they  may  throw  on 
the  coronal  variations,  and  their  pos- 
sible association  in  some  way,  not  as 
yet  detected,  with  the  Sun-spot  period. 
Even  when  a  method  has  been  de- 
vised for  observing  the  gaseous  co- 
rona, the  corona  whose  light  comes 
either  directly  or  by  reflection  from 
solid  or  liquid  matter  will  still  remain 
undiscernible  save  only  during  total 
eclipses  of  the  Sun.  Many  years 
must  doubtless  pass,  then,  before  the 
relation  of  the  corona  to  the  promi- 
nences and  the  Sun  spots  shall  be 
fully  recognized.  But  there  can  be 
no  question  that  the  solution  of  this 
problem  will  be  well  worth  waiting 
for,  even  though  it  should  not  lead  up 
(as  it  most  probably  will)  to  the  solu- 
tion of  the  mystery  of  the  periodic 
changes  which  affect  the  surface  of 
the  sun. 


II.    THE    FUEL   OP   THE    SUN.* 

Mr.Williams's  essay  opens  with  the 
argument  that  Wollaston  was  wrong 
in  regarding  the  atmospheres  of  the 
earth  and  other  members  of  the  solar 
system  as  limited.  Mr.  Williams  at- 
taches great  importance  to  this  point, 
considering  that  if  he  is  right,  all  our 
standard  treatises  on  pneumatics  and 


more  years  than  have  passed  binct 
Mr.  Williams's  theory  was  advanced, 
is  incoEsistent  with  Wollaston's  opin- 
ion, and  6  till  more  obviously  with  the 
reasoning  by  which  Wollaston  at 
tempts  to  establish  his  opinion.  The 
rather  daring  theory  of  Lu  Sage  at 
to  the  true  cause  of  gravitation  may 
be  cited  as  an  illustration  of  what  is 
undoubtedly  the  case,  that  many  be- 
fore Mr.  Williams  have  regarded  in- 
terplanetary and  interstellar  space  as 
occupied  by  matter. 

As  for  the  consequences  of  the 
opinion  maintained  by  Mr.  Williams 
(most  probably  right),  he  is,  I  take 
it,  quite  mistaken  in  supposing  them 
to  be  of  great  importance.  lie  finds 
the  objections  urged  against  his 
views,  and  Dr.  Siemens's  later  ones, 
invalid  when  once  the  atmospheres  of 
the  heavenly  bodies  are  regarded  as 
unlimited.  I  have  myself  received 
more  than  one  letter  pointing  out 
that  this  is  so.  Dr.  Siemens  himself 
is  of  course  persuaded  that  it  is.  Hut 
the  argument  is  based  on  the  mis- 
taken idea  that  because  there  is  no 
definite  limit  to  a  planet's  atmos- 
phere (or  if  there  is  no  such  limit), 
the  atmosphere  which  at  any  instant 
envelopes  a  planet  is  freely  inter- 
changeable with  the  interplanetary 
atmosphere.  But  this  would  not  be 
the  case.  Interchange  could  only 
take  place  in  accordance  with  dy- 
namical laws,  and  these  would  not 
permit  of  more  than  an  infinitesimal 
interchange  between  the  atmosphere 
immediately  surrounding  a  planet 


meteorology  must  be    remodeled.     1 1  and  the  attenuated   atmosphere   be- 
yond.    Mr.  Williams  recognizes  this 


cannot,  for  my  own  part,  see  why. 
I  doubt  very  much  whether  Dr.  Wol- 
laston's paper  has  ever  been  h*  Id  to  be 
of  great  importance,  or  whether  it  has 


as  soon  as  he  tries  to  set  his  perpetual 
solar  machine  working.  "The  Sun 
will  carry  its  own  special  atmospheric 

*  •  .  i       •  *      l  .*  I .  „ 


ever  been  regarded  as  demonstrated  ;  matter  with  it,  but  it  cannot  carry  the 
that  the  planetary  atmospheres  are  j  whole  of  the  interstellar  medium. 
limited.  Certainly  the  atomic  theory,  ,  There  must  be  a  limit  —  graduated,  no 
as  it  has  been  maintained  for  many!  doubt,  but  still  a  practical  limit  —  at 

-  j  which  its  own  atmosphere  will  leave 
.     .  azin 

"Knowledge.';    November  3    18 


*From  T*.  A.  Proctor's  scientific  magazine,   behind,  or  pass  through,  the  general 

'Ihe    atmospheric    matter."       This    ad  mis- 
^\^^   though   convenient  where  it  i. 
made,   carries  death  with  it   to  Mr. 


HUMBOLDT  LIBRARY,  No  4 


1. 


THE   SUN;  ITS   CONSTITUTION,  ETC. 


43 


Williams's  theory,  for  it  leaves  things 
praciically  as  they  would  be  if  Mr. 
Wollaston's  theory  were  unques- 
tioned. 

Mr.  Williams  conceives  the  Sun  as 
rushing  along  through  space,  gather- 
ing in  the  atmosphere  of  space  as  it 
goes,  compressing  that  atmosphere 
with  all  the  energy  with  which  a 
normally  limited  atmosphere  would 
be  permanently  compressed,  and  so 
by  its  gravitating  energy  producing 
intense  heat,  instead  of  th.it  merely 
constant  pressure  which  would  natu- 
rally result  in  the  case  of  a  constant 
atmosphere.  But  neither  the  onward 
rush  of  the  Sun  through  space,  nor 
that  swaying  of  the  Sun  around  the 
common  center  of  gravity  of  the 
solar  system,  which  Mr.  Williams 
regards  as  an  all-important  point  in 
his  theory,  could  produce  any  such 
effect.  If  we  imagine  the  Sun  with- 
out his  atmosphere,  drawing  that  at- 
mosphere in  from  surrounding  space, 
he  would  unquestionably,  in  drawing 
it  in,  produce  all  the  heat  in  which 
Mr.  Williams  believes.  And  that 
heat  might  be  stowed  away,  so  to 
speak,  iti  dissociating  the  aqueous 
vapor  so  gathered  in,  to  be  presently 
distributed  as  the  elements  recom- 
bined.  But  with  that  first  ingather- 
ing of  atmosphere  would  be  the  end 
of  this  particular  source  of  solar 
heat.  The  heat  thus  stored  could  be 
given  out,  but  no  more,  or  only  so 
much  more  as  corresponded  to  the 
exceedingly  slight  interchange  taking 
place  at  the  outskirts  of  the  solar 
atmosphere  Mr.  Williams  speaks  as 
if  the  whole  of  the  long  cylinder  of 
interstellar  atmosphere  actually  tra- 
versed by  the  Sun  were  gathered  in 
and  compressed  to  the  full  tension  of 
the  solar  atmosphere.  But  this  could 
not  happen  The  Sun  would  travel 
through  that  atmosphere,  losing  from 
his  own  (and  taking  up  from  outside 
to  replace)  only  so  much  as  friction 
at  the  outskirts  of  his  atmosphere 
would  displace. 

If  there  could  be  any  doubt,  when 
the  question  is  viewed  as  a  hydrody- 


riarnical  problem,  that  this  is  so,  it 
should  be  removed  by  the  considera- 
tion that  were  the  processes  con- 
ceived by  Mr.  Williams  to  take 
place,  one  side  of  the  sun  would  in- 
evitably present  an  appearance  differ- 
ing in  the  most  striking  manner  from 
that  of  the  other  side.  On  the  for- 
ward hemisphere,  there  would  occur 
a  constant  ingathering  of  so  much 
atmosphere  as,  when  compressed  by 
solar  attraction,  would  produoa  the 
heat  which  Mr.  Williams' 3  theory 
requires — for  note  that  the  mere  state 
of  compression  does  not  caus3  heat, 
but  only  the  forcible  compression  of 
vaporous  matter  which  had  been  un- 
compressed. All  the  heat  thus  gen- 
erated on  one  side  would  be  used  up 
in  dissociating  the  aqueous  vapor  of 
the  atmosphere  so  gathered  up.  On 
the  other  hemisphere  the  converse 
process  would  be  taking  place.  The 
dissociated  gases  would  there  rise, 
would  combine,  with  intense  emission 
of  heat,  an  i  the  products — the  cin- 
ders left  after  the  solar  firing — would 
be  flung  away  in  the  wake  of  the 
advancing  Sun.  At  least  Mr.  Wii- 
iams's  theory  requires  that  this 
ihould  happen.  Now,  astronomers 
lave  the  power  of  observing  at  one 
season  of  the  year  the  advancing  side 
of  the  Sun,  and  six  months  later  the 
retreating  side;  and  they  might  fairly 
xpect  that  regions  where  such  oppo- 
site processes  are  at  work  on  so  gi- 
antic  a  scale  would  present  a  very 
ifferent  appearance.  But  no  one 
ias  ever  yet  recognized  the  slightest 
difference  between  the  side  where  the 
Sun  is,  as  it'  were,  shovelling  in  fuel 
— turned  towards  the  Eanh  during 
the  spring  of  the  northern  hemi- 
sphere— and  the  other  side  where  he 
is  shovelling  out  cinders.  Both  sides 
look  exactly  alike. 

There  is  another  feature  of  Mr. 
Williams's  theory  which  he  specially 
defends  against  criticisms  of  mine. 
I  had  objected  that  bodies  traveling 
around  the  Sun  could  never  have 
come  into  existence  as  a  result  of 
ejections  from  the  Sun.  Granted, 


44 


THE   SlrN';    ITS   CONSTITliriON,  ETC. 


says  Mr.  Williams — though  that  was 
ncTt  exactly  the  way  lie  put  it  in 
"The  Fuel  of  the  Sun,"  I  think— if 
there  were  only  simple  ejections; 
but  if,  after  matter  has  been  ejected, 
it  explodes  like  a  rocket,  "pretty 
generally  all  around,"  a  ring  of  me- 
teors might  be  formed ;  and  he  cites 
the  behavior  of  the  colored  promi- 
nences of  the  Sun  as  showing  that 
this  actually  happens.  It  is  true  they 
often,  after  shooting  up  from  the 
Sun's  surface,  expand  laterally,  but 
there  is  nothing  in  this  more  than  we 
see  in  every  case  in  which  gaseous 
matter  is  shot  through  a  region  of 
high  pressure  into  •*  region  of  low 
pressure.  The  mauer  shot  to  a 
height  of  pay  70,000  miles  from  the 
Sun's  surface,  should  there  explode 
laterally,  so  as  thenceforward  to  cir- 
cle around  him,  the  matter  exploding 
must  divide  itself  into  opposite  por- 
tions, each  traveling  from  the  point 
of  explosion  with  a  velocity  of 
more  than  240  miles  per  second. 
Nothing  of  this  sort,  cr  approaching 
anywhere  near  this,  has  ever  been 
seen.  Moreover,  what  is  there  except 
expansive  action  to  produce  lateral 
motion  at  all  in  the  ejected  gases? 
and  how  can  lateral  expansion  do  more 
than  extend  the  expanding  matter 
until  its  density  is  equal  to  that  of 
the  atmosphere  around  it  at  the  same 
level?  In  the  case  of  terrestrial 
bomb-rockets  there  is  an  enclosing 
case  which  holds  the  explosive  sub- 
stance until,  on  ignition,  the  gases 
are  formed  which,  by  their  expan- 
sive action,  drive  out  the  particles  of 
matter  which  form  the  luminous  dis- 
play. The  circumstances  are  there- 
fore favorable  to  the  forcible  expul- 
sion of  matter.  It  is  different  in  the 
case  of  the  gaseous  matter  expelled 
from  the  Sun,  when  the  outrush  is 
over.  For  the  glowing  gas  driven 
violently  outward  on  these  occasions, 
is  not  enclosed  in  any  way.  It  is  sim- 
ply (as  the  spectroscope  shows) 
driven  up  as  a  stream  of  dense  gas 
in  a  relatively  rare  atmosphere  ;  and 
as  FOOU  as  it  can  (which  is  generally 


not  before  it  reaches  a  higher  and 
still  rarer  atmosphere;  it  expands  lat- 
erally. 

There  is  nothing  explosive  about 
this  action,  any  more  than  there  is 
in  the  lateral  expansion  of  cumulus 
clouds,  or  (which  more  nearly  illus- 
trates the  case)  in  the  outspread  of 
cloud  above  a  volcano  after  each  out- 
burst of  the  gases  which  had  been 
imprisone'd  within.  If  there  were  the 
enormous  lateral  velocities  required 
by  Mr.  Williams's  theory,  the  spec- 
itroscope  would  long  ere  this  have  re- 
vealedthem;  butwhile  it  gives  clear 
evidence  of  cyclones  low  down  in  the 
solar  atmosphere,  as  ehown  by  mo 
tions  toward  and  from  the  eyo  at  th- 
Sun's  edge,  it  has  never  shown  any 
trace  of  such  motions  in  the  glowing 
gas  flung  high  above  the  Sun's  sur- 
face. 

There  is,  however,  much  that  is 
well  worth  studying  in  Mr.  Williams's 
reasoning.  His  conclusions  seem  to 
me,  for  the  most  part,  quite  erroneous, 
but  the  evidence  he  quotes  in  their 
favor  is  deserving  of  the  most  careful 
examination. 

Mr.  Williams  considers  that  his 
views  have  been  and  are  being 
adopted  by  other  writers  on  astro- 
nomical and  physical  matters,  "  with- 
out corresponding  acknowledgment"; 
and  he  tells  us  that  in  duo  time  "an 
appendix  to  the  'Fu-.l  of  the  Sun'*' 
will  be  published  (to  a  new  edition. 
I  trust),  giving  the  particulars  of 
such  adoption.  I  doubt  the  wisdom 
of  this.  These  questions  of  priority 
are  lit  only  to  occupy  very  small 
minds ;  and  I  am  sure  Mr.  Williams 
agrees  with  me  in  regarding  all 
egotism  as  silly : — even  the  appear- 
ance of  it  is  a  thing  to  be  avoided. 
But  if  lie  does  what  he  proposes,  he 
will  have  to  be  careful  lest  peradven- 
ture  he  should  lind  the  boot  unmis- 
takably on  the  other  leg.  lie  has 
a  clear  case  against  Dr.  Siemens, 
though  I  feel  well  assured  Dr.  Sie- 
mens was  not  aware,  when  he  pub- 
lished his  theory,  how  fully  all  that 
was  sound  in  it,  and  a  great  deal  also 


THE  SUN;  ITS  CONSTITUTION,  ETC. 


that  is  unround,  had  been  anticipated 
by  Mr.  Williams.  But  in  some 
other  cases,  where  he  hints  a  suspi 
cion  that  his  views  have  been  adopted 
without  acknowledgment,  he  willn'nd 
priority  ( valeat quantum  valere  debit, 
which  is  not  saying  much)  with 
others.  For  instance,  the  theory  that 
the  larger  placets  are  miniature  suns, 
"surrounded  by  a  sphere  of  vapor, 
the  outside  of  which  we  see,"  he  in- 
cludes among  his  startling  conclu- 
sions, "utterly  at  variance  with  gen 
eral  astronomical  opinion  when  lie 
reached  them."  When  he  reached 
them  I  do  not  know,  but  I  do  know 
when  he  published  them  ;  and  I  know- 
that  several  months  before,  in  the 
winter  of  1869, 1  advanced  that  theory 
in  a  series  of  lectures  delivered  at  the 


Royal  Institution,  Manchester  (in  the  |  position  of  its  essential  points; 
svliabus    of    which  the   theory   wsis   cinnot  believe  either  that  I  a 


stated  in  so  many  words),  while  for 
at  least  \\  ye~ar  before  that,  the  prob- 
ably intensely-heated  condition  of 
the  giant  planets  had  been  dealt  with 
in  the  MS.  of  the  work  afterward 
published  under  the  title  of  "Other 
Worlds  than  Ours."  Mr.  Williams 
could  not  be  expected  to  know  about 
the  Manchester  lectures,  but  he  must 
know  enough  of  the  conditions  under 
which  books  are  published  to  be  well 
aware  that  the  chapters  on  the  giant 
planets  in  the  middle  of  that  work 
were  written,  and  even  in  type, 
before  his  -'Fnel  of  the  Sun "  was 
published.  The  theory  was  announced 
by  me  long  before.  Not  that  it  mat 
ters  in  the  least,  only :  if  such  ques- 
tions are  to  be  raised,  we  rmw  as 
well  raise  them  by  the  right  tint 

III. THE  FUEL,  OF  THE   SUN.* 

A  Reply,  by  W.  M.  Williams. 

I  must  ask  leave  to  correct  Mr. 
Proctor's  total  misapprehension  of  my 
theory  when  he  describes  me  as  sup- 
posing that  the  Sun,  after  having  ob- 
tained his  gravitation  equivalent  of 

*  From  '  Knowledge,"  I^uv.  1O,  Ioo2, 


the  universal  atmospheric  matter, 
generates  more  heat  by  merely  com- 
pressing on  one  side  and  rarefying  on 
the  other  the  same  unaltered  kind  of 
matter.  This  would  be  quite  on  a 
level  with  the  customary  paradox  of 
the  perpetual  motioners,  and  closely 
resembling  what  or.e  would  get  by  a 
pair  of  reciprocating  pistons  com- 
pressing the  air  of  one  cylinder  by 
the  elastic  expansion  of  the  other. 

Mr.  Proctor  correctly  represents 
my  view  of  the  effects  of  the  original 
aggregation  and  condensation  of  at- 
mospheric matter  about  the  Sun ;  but 
as  regards  my  attempt  to  solve  the 
great  problem  of  the  maintenance  01 
solar  energy,  he  has  not  even  crossed 
the  threshold  of  the  argument,  and 
has  evidently  "taken  as  read"  inyex- 

for  I 
am  inca- 
pable of  explaining,  or  he  of  under- 
standing, what  I  intended  to  ex- 
pound. 

The  threshold  of  the  argument  to 
which  I  allude,  and  at  which  Mr 
Proctor  halts,  is  that  the  heat  e*  olved 
by  this  origin  il  .aggregation  and  corn 
pression  would  dissociate  the  atmos- 
pheric compounds  (notably  water  va- 
por), and  thereby  store  a  reservoir  of 
heat ;  but  beyond  this,  I  have  shown 
that  the  recombination  and  explosion 
of  the  whole  of  this  is  restrained  by 
the  limitation  of  radiation  due  to  the 
"jacket"  or  envelope  of  the  chroma- 
tosphere  and  outer  atmosphere  of  the 
Sun  ;  this  limitation  determining  the 
depth  of  the  photosphere,  or  amount 
of  surface  combustion  or  recombina- 
tion. Mr.  Proctor  has  not  penetrated 
even  this,  the  vestibule  of  the  argu- 
ment. 

A  step  further  brings  us  to  that 
"swaying  of  the  Sun  around  the  cen- 
ter of  gravity  of  the  solar  system 
which  Mr.  Williams  regards  as  an  all- 
important  point  of  his  theory,"  and  of 
which  point  Mr.  Proctor  altogether 
fails  to  grasp  the  significance.  I 
maintain  that  this  produces  the  ir- 
regular angular  or  rotatory  velocities 
of  the  different  portions  of  the  solar 


46 


THE  SUN;  ITS   CONSTITUTION,  ETC. 


photosphere  which  Carrington  de- 
monstrated (the  equatorial  portions 
making  a  complete  revolution  in  { 
30  86  days,  while  those  in  latitude 
of  about  5U°  revolve  in  28-30  days), 
and  that  such  irregularity,  presuma- 
bly shared  by  the  outer  vapor  jacket, 
must  produce  vortices  or  cyclones  on 
and  about  both  bordei  s  of  the  equa- 
torial solar  zone;  that  these  vortices 
must  rip  open  that  jacket  thereabouts, 
and  thus  remove  the  restraint  to  com- 
bustion in  such  spots.  The  conse 
quence  of  this  (as  demonstrated  by 
the  laboratory  researches  of  Deville, 
Bunsen,  and  others)  must  be  explosive 
outburts  in  the  trail  of  these  vortices 
of  a  magnitude  corresponding  to 
themselves.  This  ripping  open  of 
the  solar  integuments,  and  conse- 
quent ejection  of  his  dissociated  en- 
trails, is  what  we  observe  in  the  spots 
and  prominences. 

But  what  must  follow  the  forma 
tion  of  this  partial  and  local  vacuum 
produced  by  such  ejection?  Evidently 
an  inrush  to  restore  the  broken  equi 
librium  of  general  gaseous  pressure. 
I  need  scarcely  work  out  the  pro- 
gressive steps  of  this  restoration,  first 
from  the  contiguous  gaseous  matter, 
then  from  the  further  distant,  and 
finally  from  &  portion  of  that  cylin- 
der of  interstellar  atmospheric  matter 
which  by  the  solar  translation  in 
space  is  (as  I  m  <intain),  continually 
projecting  it  elf  upon  the  Sun ;  while 
an  exact  equivalent  of  the  projected 
and  exploding  prominence  matter 
will  be  left  behind  in  the  wake  of  the 
advancing  luminary,  if  not  projected 
too  far  for  this. 

Now  we  come  to  the  source  of  re 
nenewed  energy.  It  is  simply  a  por- 
tion of  the  heat  that  has  been  ra 
diated  through  past  ages  from  all  the 
suns  of  the  universe,  and  which  1 
maintain  is  not  extinguished,  but  is 
diffused  throughout  the  interstellar 
matter.  This  is  concentrated  by  the 
solar  inspiration,  and  balances  that 
which  has  been  lost  by  his  previous 
radiations ;  for  the  ejected  gaseous 
matter  of  the  prominences  will,  when 


fully  expanded  to  the  rarity  of  inter- 
stellar atmospheric  matter,  be  colder 
than  it  originally  was,  by  exactly  as 
much  as  it  had  radiated  dining  its 
compression,  and  by  the  flaming  of 
its  re-combination.  Thus,  to  quote 
my  own  summary  at  the  end  of  Chap. 
VI.  of  the  "Fuel  of  the  Sun,"  "the 
heat  radiated  into  space  is  received 
by  the  general  atmospheric  medium  ; 
is  gathered  again  by  the  breathing  of 
wandering  suns,  who  inspire  as  they 
advance  the  breath  of  universal  heat, 
and  light,  and  life;  then  by  impact, 
compression,  and  radiation,  they  con 
centrato  Mid  redistribute  its  vitalizing 
power;  and  after  its  work  is  done, 
expose  it  in  the  broad  wake  of  their 
retreat,  leaving  a  track  of  cool  ex- 
hausted ether — the  ash-jits  of  the 
solar  furnaces— to  re-absorb  the  gen- 
eral radiations,  and  thus  maintain  the 
eternal  round  of  life." 

The  primary  agent  which  I  describe 
as  effecting  this  is  the  explosive  pro- 
jecting force  of  the  prominences.  Mr. 
Proctor  entirely  omits  this  as  regards 
its  function  in  the  maintenance  of 
solar  energy. 

Knowing  too  well  what  nn  intol- 
erable bore  a  man  may  become  when 
ventilating  his  own  theories,  I  refrain, 
at  present,  from  discussing  the  other 
points  raised  by  Mr.  Proctor,  but  will 
do  so  hereafter,  if  his  other  self,  the 
Editor  of  Knowledge,  regards  such 
discussion  as  likely  to  interest  his 
readers.  W.  M.  W. 

[I  consider  that,  apart  from  the 
interest  which  every  discussion  de 
pending  on  important  facts  must 
needs  have,  common  justice  requires 
that  Mr.  Williams  should  bo  accorded 
space  to  explain  and  defend  his  theory. 
Referring  to  his  present  remarks,  I 
note  that  he  is  mistaken  in  supposing 
I  have  "  taken  as  read  "  any  part  of 
his  theory.  He  may  not  mean  it,  but 
this  is  a  truly  painful  accusation.  1 
must  try  to  show  him  how  unjust  it 
is.  I  might  content  myself  by  assur- 
ing him  that  I  very  carefully  studied 
his  "Fuel  of  the  Sun,"  throughout, 
when  it  first  appeared,  and  recently 


THE   SUN;  ITS   CONSTITUTION,  ETC. 


as  carefully  read  the  synopsis  of  the 
theory  ;  but  this  may,  perhaps,  not  be 
sufficient.  I  would,  therefore,  invite 
his  attention  to  the  following  passage 
in  the  former  work  repeated  in  the 
latter,  "My  hypothesis  supplies  a 
perpetual  bombardment  of  165  mil- 
lions of  millions  of  tons  of  matter  per 
second,  without  in  any  degree  alter- 
ing the  density,  the  bulk,  or  any  other 
element  of  the  solar  constitution.1' 
If  this  does  not  correspond  to  the 
perpetual  motion  fallacy,  when  we 
remember  that  the  efficiency  of  this 
bombardment  must  depend  wholly  on 
the  velocity  with  which  the  Sun  trav- 
els through  space,  then  either  words 
are  meaningless,  or  for  many  years 
past  I  have  been  in  error  about  the 
very  axioms  of  mechanics.  Here  is 
a  perpetual  bombardment,  due  to  the 
Sun's  rush  through  the  interstellar 
atmosphere — so  that  his  motion  is 
perpetual  though  doing  all  this  work. 
If  I  seem  to  halt  at  the  threshold  it 
is  because  this  awful  stumbling-block 
lies  there. 

So  again,  with  the  effect  Mr.  Wil- 
liams ascribes  to  the  movement  of  the 
Sun  about  the  center  of  gravity  of 
the  solar  system.  He  thinks  I  fail  to 
grasp  the  significance  of  this  point. 
He  says  ho  "maintains  that  this  pro- 
duces the  irregular  angular  or  rotatory 
velocities  of  the  different  portions  of 
the  solar  photosphere/'  But,  as  I 
read  his  book,  he  mistakes  here :  he 
does  not  maintain  this — he  simply 
asserts  it.  There  is  not  even  an  at- 
tempt at.proof.  In  his  reasoning  about 
it  there  are  palpable  Haws.  For  in- 
stance, he  regards  the  disturbing  ef- 
fect of  Jupiter  as  about  thirteen  times 
that  of  the  Earth,  that  of  Venus  two- 
and-a-half  times,  that  of  Saturn  a 
little  above  equal — the  truth  being 
that  the  tide-raising  action  (and  the 
disturbance  in  the  solar  atmosphere 


must  be  akin  to  this)  of  Jupiter  would 
be  less  than  two-and-a-half  times  the 
Earth's,  that  of  Venus  a  little  more 
than  twice,  and  that  of  Saturn  about 
a  ninth  of  the  Earth's.  I  do  i  ofc  know, 
by-the-way,  how  Mr.  Williams  was 
led  to  suppose  that  Carrington's  re- 
searches assigned  to  the  solar  equato- 
rial regions  a  slower  rotation  than  to 
the  regions  in  solar  latitude  5!)\  He 
now  repeats  this  mistake,  which  he 
originally  made  in  the  "Fuel  of  the 
Sun."  A  slower  motion  of  the  equa 
iorial  photosphere  may  perhaps  agree 
as  well  with  his  theory  as  a  more 
rapid  motion.  (Some  theories  are  so 
fortunate!)  Still  it  checks  a  mere 
stranger,  at  the  threshold,  or  even  in 
the  vestibule,  to  find  that  an  error 
taking  off  a  fifth  of  the  equatorial 
velocity  of  the  Sun,  and  thus*  revers- 
ing its  relative  motion,  makes  no  dif- 
ference in  the  theory,  and  is  not  now, 
after  near  thirteen  years,  thought 
worth  correcting.  I  would  venture, 
however,  to  slightly  change  the  meta- 
phor, comparing  myself  rather  to  a 
surveyor  who  desires  concisely  to 
describe  the  qualities  of  a  building, 
and  who  might  well  be  content, 
though  he  had  surveyed  the  whole  of 
it,  to  note  only  the  unsoundness  of 
the  foundation. 

I  should  be  very  sorry  for  Mr.  Wil- 
liams to  suppose  I  ventured  to  critcise 
his  book  without  having  examined  it 
carefully.  I  hope  the  above  remarks 
will  show  that  I  have  noted  other 
points  than  those  touched  on  in  my 
review.  I  can  give  further  evidence 
in  the  same  direction  if  that  will  af- 
ford him  any  satisfaction  ;  but  I  must 
ask  permission  to  select  my  points. 
One  cannot  criticise  every  line  of  a 
book.  One  can  only  take  samples 
here  and  there,  unless  the  review  is 
to  surpass  in  bulk  the  work  reviewed. 
— R.  A.  Proctor.] 


CONTENTS. 


PACK. 

PREPACK       ............          •  i 

SECTION  I.  —  PURPOSE  OF  THIS  ESSAY—  DIFFICULTIES  OF  THE  SUBJECT,      .        .  2 

SECTION  II.  —  DISTANCE  FROM   EARTH  TO  SUN,           ......  2 

SECTION  III.  —  THE  DIAMETER  OF  THE  SUN,      .           ......  3 

SECTION  IV.  —  THE  FORM  OF  THE  SUN,        ........  4 

SECTION  V.  —  ROTARY  MOTION  OF  THE  SUN,         .......  4 

SECTION  VI.  —  PERTUKBATING  MOVEMENT,     ........  5 

SECTION  VII.  —  THE  SUN'S  ORBITAL  MOVEMENT,          ......  5 

SECTION  VIII.—  THE  SUN'S  ATTRACTIVE  FORCE—  DENSITY  OF  THE  SOLAR  MASS,  .  6 

SECTION  IX.  —  THE  SUN'S  ATMOSPHERE,        ........  ~ 

SECTION  X.  —  THE  CHROMOSPHERE,       .........  s 

SECTION  XI.  —  CORONA.  PROMINENCES,  AND  FACUL^E,  ......  9 

SECTION  XII.  —  THE  PHOTOSPHERE,       .........  to 

SECTION  XIII.  —  THE  SUN'S  HEAT,                ........  10 

SECTION  XIV.  —  CONDITION  OF  THE  INTERIOR  ........  M 

SECTION  XV.  —  EFFECTS  OF  HEVT  ON  MATTER  ........  n 

SECTION  XVI.  —  THE  EXPANSIVE  POWER  OF  HEAT,      .        .        '        .        .        .  i? 

SECTION  XVII.  —  Tin:  SUN'S  CRUST  ..........  M 

SECTION  XVIII.  —  THE  GASEOUS  THEORY  .....        .        .                .  u 

SECTION  XIX.  —  THK  VAPOR  THEORY  ..........  i  = 

SECTION  XX.—  THE  CLOUD-LIKE  THEORY,   ........  ;-, 

SECTION  XXI.  —  SUPPOSED  SUPPORTS  OF  THE  FOREGOING  THEORIES,  .        .        .  16 

SECTION  XXII.—  THE  CRUST  IN  A  FLUID  CONDITION  ......  20 

SECTION  XX  1  1  1.  —  PRODUCTION  OF  THE  SUN  SPOTS,     ......  2t 

SECTION  XXIV.  —  THE  AREA  OF  SUN  SPOTS  LIMITED,         i        .        .        .        .  J~> 

SECTION  XXV.  —  PERIODICITY  OF  THE  SPOTS  ........  23 

SECTION  XXVI.  —  THE  SPOTS  ARE  CAVITIES  IN  THE  SUN,    .        .        .        ;        .  24 

SECTION  XXVII.  —  How  THE  HEAT  OF  THE  SUN  REACHES  THE  EARTH,    .        .  25 

SECTION  XXVIII.  —  I'HE  QUESTION  OF  THE  EXTINCTION  OF  THE  SUN,        .        .  27 

APPENDIX.—  FIRST.—  THE  SUN'S  CORONA  AND  His  SPOTS.     By  RICHARD  A. 

PKOCTOR,      ...........  2g 


SECOND.—  THE  FUEL  OF  THE  SUN.    By  RICHARD  A.  PROCTOR,    .       42 
"  THIRD.—  THE  FUEL  OF  THK  SUN.    A  REPLY  by  W.  M.  WILLIAMS,       45 


14  DAY  USE 

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